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The effects of heterogeneity in Carbon Capture and Storage (CCS) in saline aquifers have been investigated extensively and are known to have important bearings on the storage capacity of the aquifer. In CCS projects, the time-lapse seismic survey has been proposed as a valuable tool for monitoring of CO2 movement. However, the potential of the time-lapse seismic data for heterogeneity characterization and geologic model updating has not been fully explored. One of the biggest challenges in the quantitative use of time-lapse seismic data during CCS is the complex movement of the CO2 influenced by compositional effects, geochemical reactions, phase changes and gravity segregation. In this paper, we first introduce compositional streamlines to understand and visualize the flow and transport of CO2 in the presence of mineral precipitation/dissolution, residual trapping and buoyancy effects. To start with, individual component fluxes are generated by a finite difference fully implicit compositional simulator incorporating all the relevant physics of CO2 sequestration. The fluxes are then utilized in novel streamline tracing algorithms to generate phase and component streamlines depicting the movement and the trapping of CO2 in the aquifer. Next, we utilize the compositional streamlines to determine the sensitivity of the time-lapse seismic attributes specifically, interpreted saturation differences, to changes in reservoir properties such as permeability and porosity. The sensitivities are then used in an inverse modeling algorithm to calibrate the geologic model to time-lapse seismic data. The outcome is an improved description of permeability heterogeneity that is consistent with the 4-D seismic response and improved predictions of the CO2 storage capacity. We have investigated the benefits of time-lapse seismic data integration in improving the performance assessment of CO2 sequestration using examples involving CO2 injection under realistic conditions. The first example examines the value of the 4-D seismic data integration in the estimation of storage capacity. The second example systematically studies the impact of viscous to gravity ratio on the performance of time-lapse seismic monitoring and heterogeneity characterization during CCS.

Drilling horizontal wells successfully has become one of the most important challenges facing oil companies. Horizontal wells allow operators to obtain more oil production from a single hole, compared to the cummulative production from several traditional vertical wells. New technologies have been developed to help maximize productivity in horizontal wells.A highly effective, field-proven new technology is the time-delayed filter cake removal system. The system is applied mainly in horizontal wells and can be used with different completion types including open hole, stand-alone screens, expandable screens, slotted liner, or gravel pack. The system generates organic acid downhole in a controlled manner, which dissolves all acid-soluble materials present in the mud cake throughout the horizontal interval. This breaker can be formulated to match specific well conditions and reaction delay requirements based on temperature and pressure requirements and return permeability analysis.This paper discusses the laboratory tests, planning and application processes of the system in 20 horizontal wells in Ecuador and compares the resulting productivity index of each well as a function of system design and operational parameters.

This paper shows the implementation of a workflow for quantitative use of time-lapse seismic data in computer-ssisted history matching of simulation models. The use of time-lapse seismic data alone or combined with production data gives additional valuable information about the reservoir and its behaviour. Several field examples of successful qualitative use of time-lapse seismic data exist. However a quantitative integration in the history-matching loop, considering all different types of scale along with measurement uncertainties, still represents a challenging task. We present the workflow applied in a real North Sea field case, where production data and inverted seismic data from two surveys are utilized. An implemented petro-elastic model converts from reservoir to seismic parameters. Commercial optimization software is used to minimize the difference between observed and simulated data and to update the reservoir model parameters. The main focus is to identify, understand and quantify the uncertainties in the data and the model at each step of the workflow. A key to success is tight communication and teamwork between geophysicists and reservoir engineers. Results show that including information from time-lapse seismic data in the history matching process gives us a better understanding and description of the reservoir performance and an optimized static and dynamic reservoir model.

Over 60 horizontal wells have been drilled and completed with slotted liners in Prudhoe Bay, Alaska using a low solids or solids-free clarified xanthan/brine drill-in fluid. As previously described the drill-in fluid demonstrates a functional true yield stress (TYS) in the circulating fluid.1 The yield stress is also present in the filtrate, limiting depth of filtrate invasion. The fluid has been further described as being viscoelastic (VE) under static conditions and at the low shear rates exisiting in an expanded plug flow region. This plug flow region is persistent over a wide range of flow rates and is a function of polymer concentration and brine salinity. The exhibits both time-indepent and pseudoplastic properties at higher shear rates (TIP). Collectively the viscoelastic, time-independent pseudoplastic fluid rheology is abbreviated as VETIP.1 Fluid performance has correlated to excellent well productivity, lack of formation damage, minimization of stuck pipe and liners, minimization of filter cake deposition and the lack of mud cake clean-up or removal problems, improved cost-effectiveness, and apparent improvements in present and long term well values. Lack of formation damage, near-zero stuck pipe incidence rates, and minimization of filter cake removal problems are attributed to a functional true yield stress (TYS) in the circulating fluid and filtrate. The yield stress is measurable with oscillatory (Rheometrics), capillary, constant stress, and very low shear rate rotational viscometers. New field and laboratory data correlate well to the yield stress measurements. The yield stress of the filtrate declines with time, thermal degradation, biodegradation, and is quickly broken with hypochlorite breaker, restoring original permeability, without formation damage.

Abstract This paper describes how compensated neutron and pulsed neutron logs were used to monitor performance pulsed neutron logs were used to monitor performance of a tertiary recovery minitest of CO2 miscible flooding. The paper contains (1) a description of procedures used to take and interpret the logs, procedures used to take and interpret the logs, (2) a discussion of the significance of the log responses, and (3) a discussion of the accuracy of calculated saturation changes. The experiment was run in the San Andres dolomite formation in the Willard Unit, Wasson field. Logs were taken in an observation well, completed with unperforated steel casing, and located 100 ft from the CO2 injector. Water was injected first to thoroughly waterflood the region near the observation well. This was followed by injection of CO2 and water in small, alternate slugs. Logs were taken regularly during both the waterflood and the CO2 flood. Introduction In 1972, field testing of the carbon dioxide miscible process was begun in the Willard Unit of the Wasson field in Yoakum County, Tex. Concurrently with a flood on normal well spacing, a nonproducing tertiary recovery minitest was run to get the following information:change in residual oil saturation caused by alternate CO2/water injection;extent of gravity segregation within the entire productive interval and within porous zones; and productive interval and within porous zones; andimportance of stratification and crossflow. To obtain this information, saturation changes during waterflooding and CO2 flooding were calculated from compensated neutron and pulsed neutron logs taken in an observation well; a core was taken behind the CO2-flood front with the pressure core barrel; and a history match of observation well saturation changes was made with a miscible flood simulator. This paper describes the observation well logging and its value. RESERVOIR DESCRIPTION The San Andres formation in the Willard Unit is characterized as an anhydritic, finely crystalline dolomite interbedded with subtidal or marine wackestones and packstones. Porosity and permeability development is dominated by diagenetic permeability development is dominated by diagenetic processes including dolomitization, leaching, and processes including dolomitization, leaching, and emplacement of anhydrite. Vertical flow is restricted by mudstones or by wackestones and packstones with lime mud or anhydrite filling the packstones with lime mud or anhydrite filling the pore space. Locations of wells in the minitest are pore space. Locations of wells in the minitest are shown in Fig. 1. Fig. 2 is a cross-section through these wells illustrating the continuity and highly stratified nature of the reservoir within the 160-ft pay interval. The six vertical flow barriers pay interval. The six vertical flow barriers indicated in this figure are mud-rich zones with permeabilities less than 0.1 md. We believe they permeabilities less than 0.1 md. We believe they extend throughout the minitest area. Fig. 3 shows porosities estimated from core and log data at the porosities estimated from core and log data at the 32AO well. The intervals shown by alphabetic designations are major porous zones. DESCRIPTION OF MINITEST The injection well (32A) was completed by setting casing through the formation, perforating across selected intervals, and fracturing - a typical completion technique for both injection end producing wells in the Willard Unit. The fracture was propped open with sand and had a calculated half-fracture length of 200 ft. A logging observation well (32AO) was drilled 100 ft north of the injector. In this well, casing was set through the formation but was not perforated. Another well (32AS) was drilled for fluid perforated. Another well (32AS) was drilled for fluid sampling and pressure measurements 25 ft north of the observation well. It was perforated selectively, but was not fractured. At the test conclusion, cores were taken through the entire injection interval with a pressure-retaining core barrel. The coring well pressure-retaining core barrel. The coring well (32AC) was located between the injection and observation wells.

Abstract Commercial Time Sharing Computer Services have been utilized by the headquarters staff of the author's company since November, 1967. The service has been by the General Electric Mark I and Mark II Information Processing Centers located in Dallas, Texas; Teaneck, New Jersey; and Cleveland, Ohio. Ready access to these computers by phone service through standard teletype terminals has allowed the continuous development of a fast and comprehensive group of programs for well log analysis. The ability to share the use of these programs with remote field office locations through common computer memory networks has allowed expanded application of these log analysis programs. The great flexibility and ease programs. The great flexibility and ease with which problem solutions can be programmed provides adaptability to programmed provides adaptability to unusual well log analysis problems and applications. Time shared computer programing has provided the remote user programing has provided the remote user with engineering analysis graphics with repeatable formatting, and has allowed, after the description of the program, non-technical and technical aids to accomplish well log analysis with unwavering reliability. Time sharing computer analysis has decreased the time required to do detailed well log calculations and allowed the inclusion of additional reconnaissance parameters not normally calculated during parameters not normally calculated during quick-look manual calculations of logs. Time sharing has provided an excellent tool for the company log analysts to better and more quickly serve the needs of engineers and geologists. LOG ANALYSIS BY COMPUTERS The application of computers to the calculations of log analyses is not new to the oil industry. These analyses are commonly made at the site of the computing facility which is normally staffed by computer trained formation evaluation specialists.