Coalbed Methane Resource Evaluation From Wireline Logs in the Northeastern San Juan Basin: A Case Study
- M.J. Mullen (Halliburton Logging Services)
- Document ID
- Society of Petroleum Engineers
- Low Permeability Reservoirs Symposium, 6-8 March, Denver, Colorado
- Publication Date
- Document Type
- Conference Paper
- 1989. Society of Petroleum Engineers
- 5.5.2 Core Analysis, 5.8.3 Coal Seam Gas, 1.6 Drilling Operations, 4.5 Offshore Facilities and Subsea Systems, 1.6.9 Coring, Fishing, 5.6.2 Core Analysis, 5.6.1 Open hole/cased hole log analysis
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Methane produced from coalbeds is a developing reservoir in the San Juan basin of Colorado and New Mexico. Most of the evaluation of this resource is being done by coring and testing. A cost-effective method to evaluate untested coalbeds would include using wireline logs already run through the coalbeds to assist in the evaluation process. Core analysis and production tests are essential information to use with log analysis to make meaningful evaluations from wireline logs.
This study examines 17 wells drilled in the northeastern part of the San Juan basin. These wells were drilled to produce part of the San Juan basin. These wells were drilled to produce gas from the Pictured Cliff sandstone, with the Fruitland Coal as a secondary pay zone. The objective of this study was to determine the resource potential of the Fruitland coalbeds using the available log, core and production data. The proximate analysis data from a well in which a coal core was proximate analysis data from a well in which a coal core was cut was used to calibrate the log analysis in the study area. Measured gas content data was used to calibrate the algorithm which calculated gas content from wireline data. Net coal thickness, igneous intrusive thickness, productivity potential, coal tonage per acre, average gas content and gas content per acre are the per acre, average gas content and gas content per acre are the results of this study. They are contoured to highlight the most probable area in the township to pursue coalbed methane probable area in the township to pursue coalbed methane development.
Much drilling activity in the San Juan basin of New Mexico and Colorado is in search of methane produced from Fruitland coalbeds. This new reservoir has an added advantage over other wildcat plays because it has already been logged in many thousand wells. Consequently, a large well log data base exists to map coal properties. The process of obtaining useful information from wireline logs in coalbeds is the subject of this study.
Presently, the evaluation of coalbed methane wells is being done by coring and testing. This method requires a well to be drilled, cored, completed and tested. The cost for this method of evaluating a well is quite expensive for acreage evaluation. A more cost-effective method for evaluating coalbed methane potential regionally and for planning a drilling program would be to use existing wireline logs in the prospect program would be to use existing wireline logs in the prospect area, thus generating a preliminary resource evaluation to highlight those locations with the highest probability of making a successful well. Log analysis methods have been proposed (Mullen, 1988) to help the operator evaluate coalbed methane potential from wireline logs. The information provided by log potential from wireline logs. The information provided by log evaluation includes the proximate analysis both as received and dry-ash free, the gas content of the coal (in SCF/Ton) and the productivity potential. Nothing, however, will replace having physical data to evaluate a well. But in areas where little or no core data is available, wireline data could be used to map essential coal qualities for the production of coalbed methane reserves.
This case study applies current log analysis techniques to 17 wells in the northeastern part of the San Juan Basin. These wells were drilled primarily to produce gas from the Pictured Cliff sandstone. The Fruitland coal, which overlays Pictured Cliff sandstone. The Fruitland coal, which overlays the Pictured Cliff sandstone, was considered as a possible uphole pay zone when the wells were drilled. In the study area, two wells were cored. Only one core was fully analyzed for those coal properties that provide the information needed to localize wireline log analysis. There were also three wells that are currently being produced from the coal beds.
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