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Summary Coalbeds have long been known to contain natural gas in varying amounts. To the mining industry, this is basically a hazard to be controlled and avoided where possible. To the petroleum industry, it is an exploitable resource that holds significant economic potential because of shallow drilling and the promise of long well life. The variability of coal as a gas reservoir raises the need for oil-and gas-well explorers to develop the capability of evaluating coalbed gas content to identify and produce coal gas plays. Current petrophysical models for gas reservoir analysis in traditional clastic or carbonate environments are notably inadequate for evaluation of gas content in coalbeds. However, numerous physical models exist for coals throughout the country, primarily from the efforts of the mining industry. A theoretical model was chosen and used to establish a method for evaluating gas content of coalbeds in the Black Warrior basin of Alabama. Core data in the form of proximate analysis, ultimate analysis, and gas desorption measurements were used, along with wireline data, to build the models. Results of data analysis in wells with coals ranging from low-volatile bituminous to high-volatile B bituminous are compared with core gas desorption measurements to demonstrate the accuracy of the process. The thin coals in the Black Warrior basin require high-resolution logging (especially neutron and density tools) to obtain acceptable results. Wireline computations on a prospective well can be obtained much sooner than core desorption measurements and can provide analyses in zones where samples were not recovered. Implementation of these techniques in conjunction with core measurements can help significantly in determining the economic viability of coalbed-methane prospects.

Abstract A novel combination of logs and their unique interpretations are used to improve the understanding of production in horizontal wells on the North Slope of Alaska. Two techniques using Pulse Neutron Capture (PNC) logs to identify and quantify liquid productive intervals were previously presented in a paper by Brady et. al. These techniques are compared and combined with two additional techniques:the use of time lapse LWD resistivity to determine productive intervals and liquid flow profiles while drilling, anda non trial-and-error method to determine quantitative gas production using temperature logs in a two-phase flow. Finally, modeling shows borehole gravity logs can be used to track the vertical movement of gas or water tens of feet above or below horizontal wells. Integrating the time lapse differences between the shallow LWD resistivity logs run while drilling and logs run several hours after drilling shows a strong correlation with PNC liquid flow profiles for wells producing at solution GOR. Additionally, combining a quantitative gas flow rate analysis from the temperature log with the liquid profiles provides a complete analysis of the production profile for two-phase flow in horizontal wells. Finally by combining the production profile analysis from a horizontal well with the modeled time- lapse borehole gravity data, a complete understanding of the fluid movements in the well borehole as well as tens to two hundred feet into the formation can be obtained. These techniques can be applied to both horizontal and vertical wells with both slotted liner and cemented perforated completions to obtain a quantitative production profile. The LWD resistivity data is collected while drilling to better understand the productive reservoir rock before the well is completed. Time lapse borehole gravity provides an understanding of the reservoir fluid movements affecting the wellbore flow profiles after the well has been put on production.

Colson, J.L., Schlumberger Well Services; Grau, J.A., Herron, M.M., Herron, S.L., and Schweitzer, J.S., Schlumberger-Doll Research; Hertzog, R.C.* and Preeg, W.E.,* Schlumberger Well Services; Nurmi, R.D.,* Schlumberger Middle East ; and Johnston, J.,* Schlumberger Overseas Abstract Elemental logs can be combined with mineral models to provide significant information for geological description provide significant information for geological description and evaluation of downhole formations. Mineral compositions from geochemical logs can be applied to a variety of lithologies, stratigraphic settings, and geological ages including those of the Middle East. The most abundant element concentrations in the rock forming minerals are obtained from the Geochemical Logging Tool (GLT). This tool measures natural, activation, and prompt neutron capture gamma-ray spectra. In addition to the traditional potassium, thorium, and uranium from natural gamma-ray spectrometry, a direct measurement of aluminum concentration is provided. A geochemically-based closure model is used to derive silicon, calcium, iron, sulfur, gadolinium, and titanium concentrations. The concentration of these elements, expressed in weight percent, significantly improves identification of mineral percent, significantly improves identification of mineral composition, and allows the estimation of important formation properties — an excellent basis for a broad range of applications useful to petroleum engineers, geologists, and petrophysicists. Introduction Three gamma-ray spectrometers have recently been combined into a single logging tool string to obtain elemental concentrations as a continuous function of depth for ten elements: Si, Ca, Fe, S, Ti, Gd, Al, Th, U, and K. This suite of elements has been shown to provide valuable information on the nature of the rock matrix, such as a detailed mineralogical description, sandstone classification, source rock evaluation, better porosity determination from logs, cation exchange capacity, grain-size distribution, and permeability. Much of this information could only be obtained previously through discrete core analyses. The Geochemical Logging Tool (GLT) includes measurements of natural activity for determining Th, U, and K concentrations, measurements of delayed activity induced by thermal neutron capture for determining Al concentration, and measurements of prompt gamma-rays following thermal neutron capture for determining Si, Ca, Fe, S, Gd, and Ti concentrations. While a fairly complete overall description of this tool has been presented previously, this paper provides a focus on the potential applications of geochemical logging in typical Middle East oil fields. Three examples are included to illustrate the broad range of geochemical applications:our first example of geochemical elemental concentration logging in the Middle East, taken from a clastic environment in south Oman;a second clastic example from sediments in California, similar to the problem shales that run from Egypt through the Arabian Platform into Oman and Yemen, that demonstrates detailed applications which can be derived from elemental concentration logs; anda third example from a major oil producing carbonate formation in North America that is typical of many carbonate reservoirs in the world containing a complex mixture of minerals such as those of the Arab, Khuff, Eocene of the Arabian Platform and the Kirkuk field of Northern Iraq. P. 365