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Search Petrowiki: Core analyses in tight gas reservoirs
...opment history For a long time, the Fruitland formation coals were recognized only as a source of gas for adjacent sandstones. In the 1970s, after years of encountering ...gas kicks in these coals, operators recognized that the coal seams themselves were capable of commercia...l gas rates. CBM development benefited greatly from drilling and log data compiled from previous wells ta...
Case studies can be instructive in the evaluation of other coalbed methane (CBM) development opportunities. The San Juan basin, located in New Mexico and Colorado in the southwestern U.S. (Figure 1), is the most prolific CBM basin in the world. It produces more than 2.5 Bscf/D from coals of the Cretaceous Fruitland formation, which is estimated to contain 43 to 49 Tscf of CBM in place.[1] For a long time, the Fruitland formation coals were recognized only as a source of gas for adjacent sandstones. In the 1970s, after years of encountering gas kicks in these coals, operators recognized that the coal seams themselves were capable of commercial gas rates. CBM development benefited greatly from drilling and log data compiled from previous wells targeting the deeper sandstones and an extensive pipeline infrastructure that was built to transport conventional gas. These components, along with a U.S. federal tax credit and the development of new technologies such as openhole-cavity completions, fueled a drilling boom that resulted in more than 3,000 producing CBM wells by the end of 1992. The thickest Fruitland coals occur in a northwest/southeast trending belt located in the northeastern third of the basin. Total coal thickness in this belt locally exceeds 100 ft and individual coal seams can be more than 30 ft thick.[1] The coals originated in peat swamps located landward (southwest) of northwest/southeast trending shoreline sandstones of the underlying Pictured Cliffs formation. The location of the thickest coals (Figure 1) coincides with the occurrence of overpressuring, high gas content, high coal rank, and high permeabilities in the San Juan fairway ("fairway"). The overpressuring is artesian in origin and is caused by water recharge of the coals through outcrops along the northern margin of the basin. This generates high vertical pressure gradients, ranging from 0.44 to 0.63 psi/ft,[2] which allow a large amount of gas to be sorbed to the coal. Coal gas in the San Juan basin can contain up to 9.4% CO2 and 13.5% C2 .[3] Chemical analyses suggest that thermogenic gases have been augmented by migrated thermogenic and secondary biogenic gas sources, resulting in gas contents ranging up to 700 ft 3 /ton.[4] Coal rank in the fairway ranges from medium- to low-volatile bituminous and roughly coincides with those portions of the basin that were most deeply buried. Coals in the fairway typically have low ash and high vitrinite contents, resulting in large gas storage capacities and excellent permeabilities of 10 md from well-developed cleat systems. Southwest of the fairway, Fruitland coals are typically 20 to 40 ft thick and are considerably underpressured with vertical pressure gradients in some areas of less than 0.20 psi/ft.[5]
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...the determination of lithology, net pay, porosity, water saturation, and permeability from wellbore core and log data. The chapter deals with "Development Petrophysics" and emphasizes the integration of ...core data with log data; the adjustment of ...core data, when required, to reservoir conditions; and the calibration and regression line-fitting of lo...
In making the petrophysical calculations of lithology, net pay, porosity, water saturation, and permeability at the reservoir level, the development of a complete petrophysical database is the critical first step. This section describes the requirements for creating such a database before making any of these calculations. The topic is divided into four parts: inventory of existing petrophysical data; evaluation of the quality of existing data; conditioning the data for reservoir parameter calculations; and acquisition of additional petrophysical data, where needed. The overall goal of developing the petrophysical database is to use as much valid data as possible to develop the best standard from which to make the calculations of the petrophysical parameters. Inventory of Existing Petrophysical Data To start the petrophysical calculations, the data that have been gathered previously from various wellbores throughout the reservoir must be identified, organized, and put into electronic form for future calculations.
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...hane Industry * 2.1 Characteristics of Successful CBM Projects * 2.2 Comparison With Conventional Gas Reservoirs * 2.3 Appraisal and Development Strategy * 3 CBM Reservoir Fundamentals * 3.1 What is Coal? * 3...2 Origin of CBM Reservoirs * 3.3 ...Gas Content * 3.4 ...
Development of the Coalbed Methane Industry Although mines in the U.S. have been venting coal gas intentionally since the 19th century, the production and sale of methane from coalbed wellbores is a relatively recent development. Methane was produced from a few coal seam wells in Wyoming, Kansas, and West Virginia during the early part of the twentieth century; however, the first deliberate attempts to complete wells as coalbed-methane (CBM) producers did not occur until the early 1950s in the San Juan basin of New Mexico. These wells targeted the Fruitland coal seams, which previously were viewed as a high-pressure hazard overlying deeper conventional oil and gas targets. Gas production development from the Fruitland coal seams languished until the mid-1970s when an energy crisis in the U.S. encouraged feasibility studies and investment. In the late 1970s, several companies completed wells in the Fruitland coal seams and found high gas contents and production rates of several hundred Mscf/D.[1]
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... resonance (NMR) log data can be analyzed independently or in combination with conventional-log and core data. As an independent logging service, NMR can provide porosity, permeability index, and complete...calculation * 2.2 Viscosity evaluation * 2.3 Anisotropy and geomechanics * 2.4 Low-permeability (tight) sandstones * 2.5 Heavy oil, tar sands, and tar mats * 2.6 Carbonates and complex lithologies * ...(2) where A 2.5 for water, A 1.3 for oil, and TK is temperature in K. NMR properties of gas can be obtained from published charts that relate viscosity to (1) the center of the relaxation cur...
Nuclear magnetic resonance (NMR) log data can be analyzed independently or in combination with conventional-log and core data. As an independent logging service, NMR can provide porosity, permeability index, and complete information on fluid type and saturation of the flushed zone. Some data-interpretation methods operate in the echo-decay time domain, while others operate in theT2 -relaxation domain. Estimation of residual-oil saturation is one of the oldest applications of NMR logging. Unlike resistivity-log analysis, NMR analysis does not rely on formation-water salinity to obtain water saturation.
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...gous Reservoir * 3.6 Appraisal * 3.7 Approved for Development * 3.8 Assessment * 3.9 Associated Gas * 4 B * 4.1 Barrel of Oil Equivalent (BOE) * 4.2 Basin-centered ...gas * 4.3 Basis for Estimate * 4.4 Behind-Pipe Reserves * 4.5 Best Estimate * 4.6 Bitumen * 4.7 Bu...nuous-Type Deposit * 5.23 Conventional crude oil * 5.24 Conventional deposit * 5.25 Conventional gas * 5.26 Conventional Resources * 5.27 Conveyance * 5.28 Cost Recovery * 5.29 Crude Oil * 5.30 C...
Equal to P1. Glossary of Petroleum Resources Management System - June 2018 (revised version) The sum of Proved plus Probable plus Possible Reserves.Glossary of Petroleum Resources Management System - June 2018 (revised version) The process (and associated costs) of returning part or all of a project to a safe and environmentally compliant condition when operations cease. Examples include, but are not limited to, the removal of surface facilities, wellbore plugging procedures, and environmental remediation. In some instances, there may be salvage value associated with the equipment removed from the project. ADR costs are presumed to be without consideration of any salvage value, unless presented as "ADR net of salvage."Glossary of Petroleum Resources Management System - June 2018 (revised version) Arithmetic summation of incremental categories may yield different results from probabilistic aggregation of distributions.Glossary of Petroleum Resources Management System - June 2018 ...
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...re exacting work, electrical measurements on cores will produce better numbers forn, a, and m. When core measured values are unavailable, the values of a and m inEq. 4 can be estimated as follows: in carb...andsingle well chemical tracer (SWCT) tests. These independent methods can be used to calibrate log analyses. Resistivity vs. porosity crossplots Combining Eqs. 1 and 5, the Archie saturation equation may ...ion of t into porosity is appropriate. The neutron-resistivity crossplot is not as satisfactory in gas-bearing formations as are the sonic- or density-resistivity crossplots. The apparent porosity measu...
Well logs provide insight into the formations and conditions in the subsurface, aimed primarily at detection and evaluation of possibly productive horizons. Water saturation is the fraction of the pore volume of the reservoir rock that is filled with water. It is generally assumed, unless otherwise known, that the pore volume not filled with water is filled with hydrocarbons. Determining water and hydrocarbon saturation is one of the basic objectives of well logging. All water saturation determinations from resistivity logs in clean (nonshaly) formations with homogeneous intergranular porosity are based on Archie's water saturation equation, or variations thereof.[1][2] Rw is the formation water resistivity, Rt is the true formation resistivity, and F is the formation resistivity factor.F is usually obtained from the measured porosity of the formation through the relationship For simplicity, the saturation exponent n is usually taken as 2. Laboratory experiments have shown that this is a reasonable value for average cases. For more exacting work, electrical measurements on cores will produce better numbers forn, a, and m.
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...y calculations * 2.1 Full interval as net pay * 2.2 Mobility or permeability cutoff approach * 3 Gas reservoirs * 4 Oil ...reservoirs * 5 Other historical net pay cutoffs * 6 Geologic considerations in net-pay determination * 7 Ap...FHCP, at a wellbore and its input to the overall reservoir original oil in place (OOIP) or original gas in place (OGIP) calculations. The totalFHCP at a well is the point-by-point summation over the rese...
The goal of the net-pay calculations is to eliminate nonproductive rock intervals and, from these calculations at the various wellbores, provide a solid basis for a quality 3D reservoir description and quantitative hydrocarbons-in-place and flow calculations. The determination of net pay is a required input to calculate the hydrocarbon pore feet,FHCP, at a wellbore and its input to the overall reservoir original oil in place (OOIP) or original gas in place (OGIP) calculations. The totalFHCP at a well is the point-by-point summation over the reservoir interval withEq. The top and base of the reservoir interval are defined by geologists on the basis of core descriptions and log characteristics. In the FHCP calculation, net pay, hni, at each data point has a value of either 1 (pay) or 0 (nonpay). The "net-to-gross ratio" or "net/gross" (N/G) is the total amount of pay footage divided by the total thickness of the reservoir interval (for simplicity, the well is assumed here to be vertical).
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...tively responds to the volume, composition, viscosity, and distribution of these fluids (i.e., oil, gas, and water). NMR logs provide information about the quantities of fluids present, the properties of... allow NMR data to be used to differentiate clay-bound water, capillary-bound water, movable water, gas, light oil, and viscous oils. NMR-log data also provide information concerning pore size, permeabil...le 3E.1). Whether run independently as a standalone service or integrated with conventional log and core data for advanced formation and fluid ...
Within a few years after the first successful observations of NMR in 1946, and the demonstration of free-precession NMR in the earth's magnetic field in 1948, the petroleum industry recognized the potential of NMR measurements for evaluating reservoir rocks, pore fluids, and fluid displacement (flow). In the early 1950s, several companies--particularly California Research (Chevron), Magnolia (Mobil), Texaco, Schlumberger, and Shell--began extensive investigations to understand the NMR properties of fluids in porous media for the purpose of characterizing reservoir rocks (porosity, permeability, and fluid content).[1][2][3] In addition to laboratory research, these investigations included proposals for logging devices and the development of well-logging methods to permit formation evaluation in situ.[1][4] Although a number of patents for logging tools were issued in the 1950s, it was not until Chevron completed an experimental Earth's field nuclear-magnetic-log (NML) logging device in 1958 that a functioning device was actually developed.[1][5] Limited commercial service of these devices was introduced in 1962 by Atlas, using the Chevron centralized design, and followed in 1965 by Schlumberger, using a pad-type tool of its own design. An improved version of the Schlumberger tool was introduced in 1978. Although the potential applications for this measurement were significant, particularly in the shallow, heavy-oil fields of the San Joaquin Valley,[6] in general, they did not live up to expectations and were not commercially successful.[7] Tool reliability and operational limitations proved to be major obstacles: the tool was not combinable, it required high (surface) power; the signal level varied geographically and was generally very low as a result of the low-operational frequency (2 kHz); and the borehole had to be doped with powdered magnetite to suppress the proton signal from the mud.[1][2] [8] The final version of the Schlumberger NML tool--a centralized tool introduced in 1984--proved reliable and commercially successful and was in service until the advent of modern pulse-echo tools in 1994.
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...hips * 3.3 In-Situ Density and Porosity * 3.4 Measurement Techniques * 4 Fluid Properties * 4.1 Gas * 4.2 Oil * 4.3 Brines * 5 Elasticity, Stress-Strain, and Elastic Waves * 5.1 Stress and Pressu... We consider here the properties of sedimentary rocks, particularly those that make up hydrocarbon reservoirs. Usually, these consist of sandstones, limestones, and dolomites. We must be more inclusive, and co...porates, and diatomites because these provide the seals, bounding materials, or source rocks to our reservoirs. It is important to note that shales and claystones make up the most abundant rock type in the typi...
Rock and fluid properties provide the common denominator around which we build the models, interpretations, and predictions of petroleum engineering, as well as geology and geophysics. We consider here the properties of sedimentary rocks, particularly those that make up hydrocarbon reservoirs. Usually, these consist of sandstones, limestones, and dolomites. We must be more inclusive, and consider rocks such as shales, evaporates, and diatomites because these provide the seals, bounding materials, or source rocks to our reservoirs. It is important to note that shales and claystones make up the most abundant rock type in the typical sedimentary column.
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...d laboratory observations associated with asphaltene precipitation during primary depletion and IOR gas injection follows. Aphaltene Precipitation During Primary Depletion. In normal pressure depletion, ...reservoirs that experience asphaltene precipitation usually have the following characteristics[2]: Fig. 9.1 โ... al.'s approach, EOS flash calculations with a multicomponent system are performed to obtain an oil/gas split and oil properties from which ฮฆr is calculated. This value of ฮฆr is compared with a critical ...
Several approaches that use the activity-coefficient model assume the oil and asphaltene as two pseudocomponents: one component representing the deasphalted oil and the other the asphaltenes. Andersen and Speight[69] provided a review of activity models in this category. Other approaches represent the precipitate as a multicomponent solid.
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