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The estimation of formation porosity in particular and formation volumetrics in general are key to any reservoir evaluation as they establish the hydrocarbon storage capacity. Compensated neutron porosity is one of the most common measurements incorporated in any log-based volumetric analysis. However, this type of measurement is strongly affected by the presence of trace elements, especially in clay rich formations. Trace elements, such as boron and gadolinium, have very high neutron capture cross-sections and absorb large amounts of thermal neutrons in the formation. Whenever these elements are present in concentrations exceeding just a few parts per million they have a significant effect on overall thermal neutron capture, yielding high apparent neutron porosity. When the measurement is included in an integrated log analysis system, this results in inaccurate formation porosity and matrix volumes. A reliable neutron porosity correction method is therefore needed to improve petrophysical evaluation in in such logging environments. In this work, an integrated model is proposed to correct the compensated neutron response using pulsed neutron spectroscopy measurements and other conventional log data. A joined inversion method is implemented which obtains an improved neutron response by removing the undesirable contributions by the trace elements which are not a part of the formation petrophysical model. The proposed model is validated, by applying it to several data sets from different shale plays in North America and Latin America, and comparing the results against core analysis data. Due to presence of rich trace elements in the formation, without the correction model, the original processing results indicate up to 50% higher formation porosity when compared with core measurements. After applying the proposed correction, the porosity comparison is dramatically improved, matching the reference core porosity. The proposed model offers an effective, integrated analysis method, in challenging unconventional clay-rich shale environments, for correct estimation of formation porosity and volumes of mineral constituents.

In current market conditions, performing logging operations as efficiently as practically feasible has become crucial to reduce the overall cost of formation evaluation. One of the most important formation evaluation parameters is hydrocarbon saturation. At the same time, it is imperative to obtain detailed lithological and mineralogical characteristics of the formation for optimal reservoir characterization. Acquiring all the data required for performing complete reservoir characterization from separate runs may become a time-consuming and costly activity. Typically, in openhole conditions, resistivity tools are used for determining the hydrocarbon saturation of the formation. However, when the wells are cased, conventional resistivity tools cannot be used due to the metal present in the casing. Consequently, for through-casing formation evaluation, pulsed neutron logging tools have been used for several yearsto determine hydrocarbon saturation and perform reservoir monitoring. In a high-salinity formation-water reservoir, the thermal neutron capture cross section of the formation, sigma, can be used for estimating hydrocarbon saturation. Historically, an independent deployment of a slimhole pulsed neutron logging tool was required to measure the sigma of the formation. Although the results can be very accurate, this approach is not cost-effective during the current period of oil-market downturn. Natural and pulsed neutron-induced spectroscopy measurements have been used in openhole conditions for more than a decade to determine lithology and mineralogy of the formation. In recent past, mineralogical pulsed neutron spectroscopy instruments have been characterized as tools capable of generating similar results via measurements through casing. When a mineralogical pulsed-neutron spectroscopy logging tool is used to obtain the elemental weight fractions to determine lithology and mineralogy, sigma formation parameters can also be extracted from the same measurements to provide hydrocarbon saturation. In highly saline environments, for example, chlorine, due to its high sigma response, causesa significant difference between saline-water-bearing zone and the hydrocarbon-bearing zone. Simultaneous acquisition of detailed lithology and mineralogy, along with sigma, helps in considerably reducing the logging time and completing the entire formation evaluation operation very efficiently. In addition, the acquisition capability through casing reduces health, safety &environment (HS&E) hazards. This paper demonstrates the above-mentioned methodology being applied successfully in high-salinity carbonate reservoirs in Mexico. The customer deployed the mineralogical pulsed-neutron spectroscopy tool for obtaining a detailed characterization of formation lithology and mineralogy. The same data set was used to calculate the sigma-based hydrocarbon saturation. Results showed a very high degree of agreement with conventional openhole hydrocarbon saturation analysis. These results provided the client with timely and accurate information for completion decisions. In addition, the paper shows the mineralogical results in open and cased-hole environments to illustrate the accuracy of the measurements and the proposed methodology.

Spectral gamma ray tools provide insights into the mineral composition of formations and such data can be used to distinguish important features of the formation around the wellbore. However, it is a challenge in cased-hole cases to anticipate the attenuation effects of casing within various conditions of density and thickness in an efficient manner. In this work, an innovative reduced- order Monte Carlo modelling technique is presented for cased-hole environment spectrum analysis and, specifically, to numerically determine the attenuation effects of gamma ray transmission through different materials. The presented computational method is developed accounting for different casing and cement thicknesses, and sensor positions within the borehole. The reduced order model construction could be considered one level up from the regular Monte Carlo modelling procedure as it reduces the dimensionality induced by various parameters and therefore proves an extremely useful tool handling large-scale problems that are very common in complicated downhole environment. The adjusted source distributions are then utilized to generate and validate spectra to be applied for difference logging scenarios. Two exemplary field cases are presented: 1. An open-hole logged well; 2. The same set-up well but with steel casing. The reduced modelling techniques are applied to the both cases and the possible impacts of different variable. e.g. borehole size, mud weight and cement thickness on the sensor-obtained spectra are discussed. Future work will involve a series of case studies .e.g. the sensitivity assessment of formation impurities and an extension of the Monte Carlo computed elemental standards to a great variety of nuclear downhole sensor designs.

A systematic computational method for obtaining accurate elemental standards efficiently for varying borehole conditions was developed based on Monte Carlo simulations and computational data assimilation. Elemental standards are essential for spectral unfolding in formation evaluation applications commonly used for nuclear well logging tools. Typically, elemental standards are obtained by standardized measurements, but these experiments are expensive and lack the flexibility to address different logging conditions. In contrast, computer-based Monte Carlo simulations provide an accurate and more flexible approach to obtaining elemental standards for formation evaluation. The presented computational method recognizes that in contrast to typical neutron-photon simulations, where the source is typically artificial and well characterized [Galford, 2009], an accurate knowledge of the source is essential for matching the obtained Monte Carlo elemental standards with their experimental counterparts. Therefore, source distributions are adjusted to minimize the least square difference of the Monte Carlo computed and experimental standards. In this work, a natural gamma ray spectroscopy tool is selected as an example and the procedure of obtaining elemental standards through Monte Carlo modelling and data assimilation is demonstrated. A field case study is presented to compare two sets of elemental standards. For future work, the adjusted source distributions will be utilized to generate and validate spectra for varying borehole conditions: tool position, casing and cement thickness and the effect of these conditions on the spectra will be investigated. Given that Monte Carlo modeling provides much lower cost and more flexibility, employing Monte Carlo could enhance the processing of nuclear tool logging data computed standards.

Laparoscopic pyeloplasty (LP) is gaining acceptance as a standard of care for the repair of ureteropelvic junction (UPJ) obstruction, with results comparable to those of open repair. However, it remains a technically challenging procedure requiring intracorporeal suturing skills. Recent reports have demonstrated equally effective results with robot-assisted laparoscopy with shorter operative times. We present our modified technique for daVinci robot-assisted LP.From November 2002 to May 2004, 32 consecutive patients underwent LP with the daVinci robotic system for UPJ obstruction. Just prior to laparoscopy, 31 patients underwent retrograde pyelography and cystoscopic placement of a ureteral catheter just distal to the UPJ, which was prepared into the operative field. The remaining patient had an indwelling stent placed preoperatively. Three transperitoneal ports are placed for the robot. A fourth port is placed for retraction, suction, dissection, and suture passage by the bedside surgeon. This port was placed at McBurney's point in the first two patients and the subxiphoid area in the subsequent 30 patients. A ureteral stent was inserted retrograde intraoperatively with laparoscopic assistance after exchanging the ureteral catheter for a guidewire. A Jackson-Pratt drain was placed in all cases.All procedures were completed laparoscopically. Anderson-Hynes dismembered pyeloplasty was performed in 31 patients, while Fengerplasty was performed in 1 patient. The average operative time was 300 minutes (initial 12 procedures: 384 minutes; last 10 procedures: 197 minutes). The average blood loss was approximately 50 mL and the average hospital stay 1.1 days. A crossing vessel was present in 44% of the cases. Stone extraction was performed in 5 cases (23%) and kidney biopsy in 1 case. The only perioperative complications were one migrated stent, which was repositioned under sedation without sequelae and one urinary tract infection. Of the 18 patients with follow-up exceeding 6 months (average 10.3 months), 16 have improved drainage and function and are asymptomatic. One patient with flank pain has no evidence of obstruction. One with delayed, although improved, drainage is asymptomatic.The daVinci robot system can be used effectively for LP. Although initial operative times were long, there was a significant decrease after the first 12 cases. Having retrograde access to the ureter allows simple intraoperative stent placement. We found that the subxiphoid placement of the fourth port gave the bedside surgeon the optimal location for suction, dissection, and intracorporeal suture passage. This approach and technique have become standard in our treatment of UPJ obstruction.

As laparoscopic surgery has evolved, it has become part of the urologic surgical armamentarium and is now used to perform more complex procedures. Carbon dioxide, used to create pneumoperitoneum, produces physiologic changes in various organs, including the kidneys. Such changes are associated with altered redox status because of the release of free radicals and changes in oxidative stress signals. It is unknown whether prolonged pneumoperitoneum is associated with an increase in oxidative stress compared with open surgery. The objective of this study was to compare oxidative stress in patients undergoing urologic laparoscopic and open operations.Urine samples were obtained immediately preoperatively, immediately postoperatively, and at 6 and 18 hours after surgery from 10 patients who underwent urologic laparoscopic surgery and 10 patients who underwent open surgery. Concentrations of the oxidative stress marker isoprostane (8- iso-prostaglandin F2a) were measured, and the results were analyzed with respect to clinical factors associated with the type of surgery.Urinary isoprostane concentrations (mean +/- SEM) in the laparoscopic and open groups showed an increase immediately after surgery to 189.0 +/- 64.2% and 141.1 +/- 45.8% of the preoperative values, respectively. A decrease in isoprostane was subsequently observed in both groups at 6 hours postoperatively, with preoperative values restored at 18 hours postoperatively (126.3 +/- 19.7% and 89.5 +/- 55.9% at 6 and 18 hours, respectively, in the laparoscopic group and 130.7 +/- 41.6% and 88.7 +/- 20.4% at 6 and 18 hours, respectively, in the open-surgery group). Although in both groups the peak PGF 2a concentration was observed immediately (0 hours) postoperatively, no significant differences were observed between the groups at 0, 6, and 18 hours. In the laparoscopic-surgery group, the mean increase tended to be higher and the decrease to be less prolonged than in the open-surgery group.Oxidative stress, as measured by urinary 8-iso-prostaglandin F2a, is produced by both laparoscopic and open urologic surgery. The findings of our nonrandomized study suggest a pattern of increased oxidative stress postoperatively with either type of surgery, with subsequent return almost to preoperative levels. Prolonged laparoscopic operative time did not affect oxidative stress levels.

Living-donor nephrectomy has traditionally been performed through a flank incision with or without rib resection or by an anterior extraperitoneal incision, both of which reduce the willingness of potential donors to undergo the procedure. The first successful human laparoscopic donor nephrectomy was reported in 1995. In order to reduce warm ischemia and operative time and to make the operation safer and easier, some laparoscopic surgeons have used hand assistance. The authors describe their technique for this operation and review the results.

Multiple myeloma is characterized by neoplastic proliferation of a single clone of plasma cells engaged in the production of a monoclonal protein. This condition affects mainly the bone marrow, but extramedullary manifestations can be seen in any organ. Urinary bladder involvement is extremely rare, with only 14 cases reported in the literature to our knowledge. Herein, we report a large extramedullary bladder plasmacytoma arising in a patient with history of multiple myeloma. A 78-year-old woman with history of multiple myeloma, currently in remission, presented with a large intravesical tumor. Because the tumor was considered to have characteristics of anaplastic neoplasm from transitional cell origin with evidence of deep muscular invasion, a radical cystectomy was performed. A subsequent microscopic evaluation of the cystectomy specimen revealed round cells with an eccentric cartwheel-like nucleus suggestive of plasmacytoma. The diagnosis was further confirmed with immunohistochemical studies. It is difficult, according to the literature, to distinguish bladder plasmacytoma from anaplastic transitional cell tumors. It is important to provide the pathologist with an appropriate history and to have a high index of suspicion for bladder plasmacytoma in patients with previous diagnosis of multiple myeloma and bladder mass.

Partial nephrectomy is currently recommended for most amenable solid renal tumors, especially if they are exophytic and less than 4 cm. We reviewed our initial experience with laparoscopic partial nephrectomy for solid renal masses without clamping the renal vasculature using a monopolar device that uses radio frequency energy with low volume saline irrigation for simultaneous blunt dissection, hemostatic sealing and coagulation of the renal parenchyma (TissueLink, TissueLink Medical, Inc., Dover, New Hampshire).From September 2002 to April 2003, 10 patients underwent transperitoneal laparoscopic partial nephrectomy, including 9 with solid renal masses and 1 with a complex cyst. In all cases the renal hilum was dissected and the renal vessels were isolated but none had renal vascular clamping. The TissueLink DS dissecting sealer or Floating Ball (TissueLink Medical, Inc.) was used to dissect the tumor free bluntly, while simultaneously sealing and coagulating bleeders.Mean patient age was 54.6 years (range 42 to 72). Mean American Society of Anesthesiologists score was 2.3 (range 2 to 4). Mean tumor size was 3.9 cm (range 2.1 to 8). The mass had a peripheral location in 7 cases and a central location in 3. Mean operative time was 232 minutes (range 144 to 280) and mean blood loss was 352 ml (range 20 to 1000). One patient received blood transfusion and all tumor margins were negative. Mean hospital stay was 1.7 days (range 1 to 5) and pain medication use was minimal. One patient had a brief period of urine leakage from the lower pole calix, which was managed successfully by ureteral stenting and Foley catheter drainage of the bladder.Laparoscopic partial nephrectomy can be performed without renal vascular clamping. TissueLink technology allows complete tumor resection and provides adequate parenchymal hemostasis of the tumor bed. Its scant tissue charring production does not interfere with the pathological assessment of the tumor margin status.

Formation mineralogy is fundamentally important to the proper characterization of carbonate reservoirs. Knowledge of the dominant calcite and dolomite components, as well as the anhydrite evaporitic precipitate component, is important to the assessment of carbonate petrophysical properties. Core samples have always provided an excellent but time consuming source for carbonate formation mineralogical data. Now such information can be obtained — continuously and rapidly in carbonate formations — using modern nuclear logging tools that incorporate the principles of natural and induced gamma ray spectroscopy. The calcium, carbon, magnesium, and sulfur elemental concentrations — from the inelastic and capture spectra of the pulsed-neutron spectroscopy tool — provide the data required to compute formation quantities of calcite, dolomite and anhydrite.Accurate quantification of low concentrations of the quartz, illite, feldspar, and mica (QIFM) silicate mineral phases — present in carbonates as a result of windblown clastic influx — is important for carbonate net pay delineation and time stratigraphic layer models. The dilute QIFM is indicative of aerial exposure-related carbonate diagenesis and low sedimentation rate carbonates, which may be porous but impermeable. Core studies of important carbonate sections obtained and previously published (Clerke, 2009; Clerke et al. 2008; Clerke, 2004; Kamal et al., 2004, Clerke, 2003) show that the amounts of aluminosilicate material within these carbonate formations are typically less than 10%, but that important carbonate textural changes are associated with small variations in the abundance of QIFM.This work investigates the combination of the FLeXSM (Formation Lithology eXplorerSM) geochemical outputs of silicon, aluminum and iron — coupled with the potassium output from the natural gamma ray spectroscopy tool. The combination of these elemental outputs provides a high accuracy and high precision QIFM abundance at low concentrations in carbonate formations. Within typical carbonate formations, this combination is shown to provide data quality and accuracy over the range of 1-5% QIFM with a statistical precision of less than one percent. This is demonstrated using computer simulations of the FLeX tool performance, in addition to measurements in numerous laboratory carbonate-block formations. The mineralogies of the test-block formations are obtained by using XRD and XRF analysis. The computer simulations of tool performance use Monte-Carlo generated elemental concentrations that are then converted to mineralogy, using the software employed in well log processing of subsurface FLeX data.This paper demonstrates the ability of the tools’ combined elemental signals to provide accurate and precise volumes of low concentration (1-5%) QIFM silicate material in a predominantly carbonate formation. This ability is an important and economically-leveraging technical development, with application to the carbonate reservoir quality modeling of the Middle Eastern Khuff gas-bearing formation, in addition to other Permian age formations in the West Texas basins. Accurate identification and quantification of the QIFM mineralogical component of the rock matrix provides an important input for refined models of carbonate reservoir quality, diagenesis and aerial exposure, as well as serving as a utility for time marker beds in stratigraphic reservoir models.

Due to environmental concerns, the use of radioactive chemical sources is discouraged. This presents great challenges for conventional practices. Source-free logging tools, such as Nuclear Magnetic Resonance (NMR) and acoustic tools, have also been used for porosity determination. However, sometimes uncertainties in lithology, mineralogy, and/or fluid properties can result in unacceptably large error bars in porosity by either NMR or acoustic logging alone. Integrating acoustic and NMR measurements for gas-zone porosity estimation has been reported in relatively clean sandstones. The existing method in literature has not been extended to shaly sandstone reservoirs or carbonate formations where clay is also present. We developed a new, practical sourceless porosity-estimation method which uses NMR log to calibrate the acoustic porosity model and which corrects shale effect on acoustic porosity. To apply this method, both clean and shaly water-bearing intervals are selected for calibrating acoustic model parameters. By applying the calibrated model, dry matrix slowness on each depth in the gas-bearing interval can be obtained. Porosity can then be determined by introducing the computed dry matrix slowness to Raymer-Hunt-Gardner transform for the gas-bearing interval. This method has been successfully tested on a number of wireline and LWD logs. In this paper are two case histories; one case study involves a shaly sand reservoir, and the other, a low-porosity carbonate reservoir. For both cases, the sourceless porosity is cross-validated with other approaches for both the water-bearing and gas-bearing sections.

The successful recovery of hydrocarbons from gas shales requires a fundamental understanding of the reservoir's rock-matrix properties. Information about the variable lithologies, mineralogies, and kerogen content is vital to locate favorable intervals for gas production. Knowledge of the in-situ stresses and porosity of these intervals is essential for developing hydraulic fracturing strategies to recover the gas in place. Often these properties are established from the analysis of cores extracted from the wellbore, a time-consuming practice which causes costly delays in well completions and prolonged rig time. We demonstrate that these reservoir rock properties can be measured and predicted in-situ from the wellbore environment by a formation evaluation method that employs a combination of measurements made by downhole geochemical, acoustic, and nuclear magnetic resonance sondes. Using this combination of tool measurements we determine lithology, mineralogy, and kerogen content. The mineralogy, porosity, acoustic velocities, bulk density, pore pressure, and overburden stress are then used to compute the unconfined compressive strength, Poisson's ratio, and horizontal stress for each interval. These results can then be used to develop hydraulic fracture strategies. The effectiveness of this approach is shown through characterization of the rock properties of the Caney and the Woodford Shale from three different wells. The ability to quantify the kerogen content from these formations is emphasized as there is currently no other direct quantification of carbon from openhole wireline logging available. This approach for characterization of shale gas reservoirs is also further supported through comparisons of core data that display the mineralogy, chemistry, kerogen content, and geomechanical properties from the wellbore section.

The assessment of reservoir productivity and subsurface hydrocarbon can be significantly enhanced through an understanding of formation mineralogy and organic carbon. Such information allows petrophysicists to resolve ambiguities in their predictions of reservoir hydrocarbon potential. While core samples are a prime source for exact formation mineralogy, excellent results can also be derived in a timely and cost-efficient manner from in-situ log chemistry measurements of the rock. A direct measurement of the formation's elemental concentrations is achieved using a gamma ray scintillation sensor in combination with a 14-MeV pulsed-neutron generator. The most important element measured is carbon, as it may provide a direct indication of reservoir hydrocarbons. This paper presents a method for determining the amount of organic carbon in subsurface formations using a pulsed-neutron mineralogy tool and a natural gamma ray spectroscopy tool. The natural, inelastic, and capture gamma ray energy spectra from these instruments are used to extract the chemistry of the subsurface formation being investigated. The elemental concentrations measured include Al, C, Ca, Fe, Gd, K, Mg, S, Si, Th, Ti, and U. Carbon is very difficult to measure without the inelastic spectrum generated from a pulsed-neutron source. An interpretation process, based upon the geochemistry of petroleum-bearing formations, is employed to derive the lithology and mineralogy which leads to the interpretation of the carbon measurement. The oil saturation can be computed in conventional reservoirs, assuming that the amount of carbon in excess of that required for the inorganic matrix mineralogy is part of the pore fluid as hydrocarbon. The direct carbon measurement is also important in laminated shaly sands or in low-salinity reservoirs, where oil saturation determination from indirect measurements, such as resistivity, is not compatible with the environment. In other formations the carbon can be determined to be a component of the rock matrix as kerogen or coal, both of which are uniquely identified with this logging system. Kerogen becomes extremely important in the evaluation of shale gas formations. Field examples are presented to illustrate the effectiveness of the carbon measurement.

Well log data provides valuable information for characterizing reservoirs through seismic analysis, reservoir modeling and fluid substitution. Reliable economic evaluation of a reservoir demands reliable characterization of reservoir properties. It is crucial to have a reliable uncertainty analysis for non-unique solutions of reservoir characterization. A stochastic petrophysical model based on an inversion algorithm was used to compute reservoir properties. The well log data uncertainty and the resulting impact were studied with an error propagation algorithm. The algorithm was presented to calculate propagated error and manage uncertainties based on Gassmann's fluid substitution. Data control for the input measurement of Gassmann's equation was performed through environmental uncertainties analysis before proceeding with the inversion. To demonstrate the error propagation in reservoir characterization, we studied both in-situ and dry models before fluid substitution. Then, the uncertainty analysis was performed for the new model with fluid substitution. Moreover, the propagated errors for velocities of the new model were also evaluated. A joint interpretation based on a volumetric mathematical model of various logging measurements was used to analyze data quality. In this paper, we present an important insight into uncertainty analysis and error propagation in fluid replacement modeling. The algorithm provides stable solutions with uncertainty control for reservoir characterization.

Gas shales are economically viable hydrocarbon prospects that have proven to be successful in North America. Unlike conventional hydrocarbon prospects, gas shales serve as the source, seal, and the reservoir rock. Generating commercial production from these unique lithofacies requires stimulation through extensive hydraulic fracturing. The absence of an accurate petrophysical model for these unconventional plays makes the prediction of economic productivity and fracturing success risky. This paper presents an integrated approach to petrophysical evaluation of shale gas reservoirs, specifically, the Barnett Shale from the Fort Worth basin is used as an example. The approach makes use of different formation evaluation data, including density, neutron, acoustic, nuclear magnetic resonance, and geochemical logging data. This combination of logging measurements is used to provide lithology, stratigraphy and mineralogy. It also differentiates source rock intervals, classifies depositional facies by their petrophysical and geomechanical properties, and quantifies total organic carbon. The analysis is also employed to locate optimal completion intervals, zones preferable for horizontal sections, and intervals of possible fracture propagation attenuation. Resistivity image analysis complements the approach with the identification of natural and drilling induced fractures. We compare results from three different wells to show the effectiveness of the method for shale gas characterization. The methodology presented provides a means to understand the geomechanical and petrophysical properties of the Barnett Shale. This knowledge can be used to design a selective completion strategy that has the potential to reduce fracturing expenses and optimize well productivity. Though developed specifically for the Barnett Shale, the underlying ideas are applicable to other thermogenic shale gas plays in North America.

[1] An accurate description of water- or oil-bearing reservoirs strongly depends on a robust determination of their petrophysical parameters, e.g., porosity, permeability and fluid distribution. Downhole logging measurements are the primary means to formation evaluation; however, they do not directly provide the petrophysical properties of interest. To interpret well logging data, a range of empirical models are usually employed. These empirical relationships, however, lack scientific basis and usually represent generalizations of the observed trends. Since macroscopic rock properties vary depending on their microstructure, we suggest using a pore-scale approach to establish links between various petrophysical properties of sedimentary rocks. We outline a method for computing formation permeability using the proposed rock models. The method utilizes NMR (Nuclear Magnetic Resonance) logging data for the information about porosity and grain size. We also present an approach for prediction of acoustic velocities of model rocks. The proposed methodology is applied to the field data, and the corresponding interpretation results are included in this paper.

The surgical treatment of urinary tract calculi has changed enormously during the past two decades. With advances in fiberoptics, development of flexible instrumentation, and the widespread use of extracorporeal Shockwave lithotripsy (SWL), open stone surgery (OSS) has mostly been replaced by minimally invasive procedures for managing both renal and ureteral calculi.

Reconciling formation porosity and fluid distribution estimations in carbonate and shaly-sand systems represents a problem that log analysts and petrophysicists face in dealing with well log interpretation. The problem becomes especially challenging when data from conventional (e.g., density, neutron, gamma ray) and non-conventional (e.g., Nuclear Magnetic Resonance (NMR), multi-component induction) instruments are available and need to be combined in a consistent interpretation. Also, the use of effective and/or total porosity petrophysical models may lead to confusion and improper use and interpretation of those quantities. The paper proposes petrophysical interpretation models for use in the evaluation of carbonate and shaly-sand reservoirs. They allow for effectively and consistently combining the various measurements under the framework of either effective or total porosity. Simultaneous and sequential solutions of the petrophysical models are proposed leading to consistent data integration and reconciliation of porosity and fluid distribution across the various available log measurements. The proposed interpretation method focuses on the integration of NMR with conventional log measurements in carbonate and shaly-sand environments. With sufficient log data, rocks having complex mineralogy can be interpreted in terms of mineral volumes, irreducible and moveable water saturation, and hydrocarbon saturation. In a shaly-sand environment, results are expressed in terms of sand, shale and fluid saturation distributions. The paper describes the mathematical formulation of the petrophysical model as well as the applied numerical techniques. Optimal interpretation results are achieved using forward modeling and a constrained, quality-weighted error minimization technique. Field data examples are presented that show the ability of the interpretation models to reconcile porosity, fluid type, and fluid distribution in the pore space.

A new openhole logging service, RockViewSM, has been developed which provides lithological and quantitative mineralogical information for accurate formation evaluation. The assessment begins with elemental formation weights and follows with an interpretation of lithology and mineralogy. Lithologies are divided into general categories including sand, shale, coal, carbonates, and evaporites. Potentially identifiable minerals are quartz, potassium-feldspar, albite, calcite, dolomite, siderite, anhydrite, illite/smectite, kaolinite, glauconite, chlorite, pyrite, and others. The logging system utilizes an electronic pulsed source to send high energy neutrons into the surrounding formation1-8. These neutrons quickly lose energy as a result of scattering, after which they are absorbed by the various atoms within the ambient environment. The scattered as well as the absorbed neutrons cause the atoms of the various elements to emit gamma rays with characteristic energies. These are measured with a scintillation detector, resulting in both inelastic and capture gamma ray energy spectra. A matrix inversion spectral fit algorithm is used to analyze these spectra in order to separate the total response into its individual elemental components. The prominent measured elements associated with subsurface rock formations include calcium, silicon, magnesium, carbon, sulfur, aluminum, and iron. Potassium, thorium, and uranium are measured separately with a natural gamma ray spectroscopy instrument9-11. The tool response is characterized for each individual element by placing it into formations of known chemical composition. Interpretation of the data begins with an assessment of the elemental formation weights, which then leads to a determination of lithology and mineralogy. Each step in the process is guided by the examination of ternary plots containing selected elements. Magnesium is an extremely important part of the interpretation process since it distinguishes dolomite from calcite and helps to identify various types of clay. Data from field examples is presented in order to illustrate the effectiveness of this technology.

Background Laparoscopic living-donor nephrectomy has gained acceptance within the transplant community. The technique requires advanced laparoscopic techniques, and great care must be taken to ensure safety of the operation for the donor and transplantability of the donor kidney. Minimizing the risk of bleeding and trauma to the kidney are important features of a successful living-donor nephrectomy. Improved laparoscopic instrumentation has afforded greater safety and efficacy through technical advances. Methods The LigaSure device was used in 124 consecutive living-donor nephrectomies beginning in 1999. A transplant database was reviewed for operative statistics including intraoperative blood loss and operating time. Results The LigaSure device was used to dissect and seal all venous and arterial branches. Estimated blood loss was 90 +/- 53 mL. A suction device was required in only 40 (32%) of the cases. No patient experienced postoperative bleeding. There were two donor complications: one incisional hernia and one ileus. All kidneys functioned immediately upon reperfusion. Conclusions The LigaSure device is an extremely effective tool for obtaining hemostasis by sealing both venous and arterial branches of the major renal vessels. This is also effective in sealing lymphatic tissues and thereby facilitating dissection. Avoiding the use of metallic clips simplified final division of the renal artery and vein. As with any laparoscopic instrument, the anatomic geometry of the operative field may limit use based upon port placement.

Several different procedures can be used to treat UPJ obstruction. Retrograde ureteroscopic endopyelotomy provides a safe and adequate first line of treatment for this condition. With the advent of smaller ureteroscopes and ancillary devices, this technique has evolved to include children. Adherence to strict endourologic principles and direct visualization make retrograde ureteroscopic endopyelotomy a safe and effective treatment modality. This procedure represents an extension of the basic endoscopic skills of the urologist, creating a short learning curve and wide margin of safety.