TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes the application of a practical technique to determine infill potential when faced with little time, large data sets, and complex geology. Using this technique, we determined where newer wells are encountering potentially depleted reservoir and the infill potential for the Milk River formation within a 900-well, 200,000-acre area in the Western Canada Sedimentary Basin. We obtained these results in a minimal amount of time and used only monthly production and wellbore location data. We validated our technique by "history matching" the production performance of recently drilled wells. We correlated well quality with historical well densities in order to predict the infill well potential from 160acre spacing to an 80-acre well spacing. We estimated ultimate recoveries for all existing wells and infill candidates and show their reserve distributions. We identified 896 infill candidates with 8.9 X 10 9 m 3 of gas reserves. The results of this study are presented in this paper using tables, graphs, and maps.The results of a study applying this analysis technique can be used when budgeting and planning near-and long-term drilling programs. The analysis techniques described in this paper could be applied by operators in other areas and reservoirs to evaluate their own acreage position or infill drilling potential.
The major objective of this paper is to identify the most generally applicable method to analyze pressure transient tests in coalbed methane reservoirs. The desired methodology should allow us to analyze short term pressure tests and long term performance data consistently and in a way that can lead to an adequate reservoir description. An important part of this work was the evaluation of the methods currently proposed in the literature for estimating properties of coalbed methane reservoirs. The paper identifies the assumptions and data requirements for the conventional (i.e. Perrine-Martin) method and pseudopressure method of Kamal and Six along with their potential range of applicability in coalbed methane reservoirs. The paper compares the results using the analytical solution methods to the results obtained with a 2-phase, 3-dimensional, finite difference simulator. We show that oversimplifying or neglecting desorption of methane from the coalbed methane reservoir matrix as is done in the analytical methods can lead to inaccurate estimates of permeability. Thus, we concluded that the only generally trustworthy method of analysis of transient and longer-term production data is to use a coalbed methane simulator which includes diffusion and desorption. Another objective of the paper is to validate the method chosen for estimating permeability in a coalbed methane reservoir at a specific geologic location using actual field data. We developed a coalbed methane reservoir description by history matching actual production and pressure data. We compared the permeability values from the simulator to those estimated from the analytical solution methods and found that the analytical methods do not provide accurate estimates of permeability for this field example. The oversimplified assumptions used in the development of the conventional and pseudopressure methods have a significant influence on the permeability estimates and cause inaccurate results.
The measurements available to estimate reservoir parameters are numerous, yet most wells are completed in various shales without traditional log measurements. Horizontal wells continue to be drilled, and while the number of stimulation stages pumped per lateral length continues to increase, many questions remain: Is there an increase in production commensurate to the added cost, or will it soon become unsustainable? Would better characterization of the effective surface area after hydraulic fracture stimulation help explain the reservoir potential? Analysis of production data from fractured shale gas wells is difficult. Operators try to estimate fracture and reservoir properties for a horizontal well with multiple hydraulic fractures by using pressure transient testing, even though in reality it could take 10,000 years for the actual reservoir pressure to be measured. Alternatively, others model the production of fractured shale gas reservoirs from a zone-altered permeability area, which may be quite limited in areal extent but is surrounded by a low-matrix-permeability reservoir to account for the well productivity. Ultimately a simplistic reservoir model for production forecasting uses whatever data is available and our basin experience. How do we validate these models? Traditionally we look at case studies to find an analogous situation to validate and identify the dominate production drivers. Existing approaches to model shales require years of production data, and even then they cannot uncouple reservoir properties from completion parameters to help optimize flow efficiency. When production is measured on a stage-by-stage basis, and laboratory and log analysis data are presented for reservoir and fluid characterization, solving for the created effective surface area should be straightforward. By better characterizing along the wellbore and by discriminating the contributions of RQ and CQ to the reservoir production, we will be able to better predict long-term well production and better understand the reservoir potential. This paper discusses the current status of production prediction for shale gas reservoirs and provides a vision of possibilities for better interpretation, i.e these production models must go hand-in-hand with hydraulic fracture models to determine the crucial parameters that drive production, thus fully optimize well and field production.
SPE Members Abstract This paper presents the development of a coalbed methane reservoir description from the analysis of production and pressure transient data for a producing open hole cavity well and two observation wells completed in the Fruitland Formation in the San Juan Basin, Colorado. Data collected and evaluated include open hole drill stem tests and a post-fracture pressure buildup test for the observation wells and multi-well interference tests and pre- and post-cavitation pressure buildup tests and production data for the cavity completed well. The main objective of the work presented in this paper was to gain a better understanding of the mechanisms controlling gas production from open hole cavity completion wells. The recent emphasis on evaluating the productivity of open hole cavity completion techniques relative to the productivity of cased hole hydraulically fractured completion techniques makes this reservoir characterization important. A good reservoir description may help quantify an increase in the effective permeability, if any, of the coal natural fracture system and help us to understand the reservoir conditions where cavitation may be a suitable stimulation technique for coalbed methane reservoirs. Suitable reservoir conditions may include high permeability, high pressure or a combination of the two. On the basis of the data analyzed, we found that the open hole cavity completion appears to be characterized best with a reservoir description where an altered zone of higher permeability is present around the radius of the cavity to account for the increase in gas production. We will demonstrate that our reservoir description is reasonable by showing a history match of pressure transient and production (gas and water) data both prior to and after the creation of the cavity. We determined the permeability anisotropy of the reservoir natural fracture or cleat system through the analysis of the pre-cavitation interference tests. The geometry and magnitude of the altered zone were determined by matching the post-cavitation pressure profiles of the observation wells. We verified the reservoir description by comparing a production forecast based on this description with observed long term data. This study provides a reservoir description that illustrates how a cavity completion can dramatically improve the productivity of a coalbead methane well. Introduction The Gas Research Institute (GRI) sponsored a research program in the Fruitland Formation in the San Juan Basin to study the effects of open hole cavity completions on the productivity of coalbed methane wells. Three wells were drilled in an area termed the Completion Optimization and Assessment laboratory (COAL) Site. Two wells were drilled as observation wells and the third well was completed with an open hole cavity. Well tests were performed on each of the three wells to estimate reservoir properties. For the cavity completed well, the benefit of cavitation was obvious. P. 269^
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