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Description of the material:
When assessing environments for methane production from hydrates, constraining methane hydrate phase equilibrium behavior in sediments is instrumental in understanding and predicting subsurface hydrate distributions. We integrate log and laboratory data from shallow sediments in the Nankai Trough offshore Japan to determine pore size and its effect on methane solubility.
Our work shows how pore size affects the quantity of methane dissolved in pore fluid in Nankai Trough sediments. Understanding methane availability and distribution is an important component of prospect assessment and completion design in hydrate plays. This method may be used to predict methane hydrate stability conditions from wireline or LWD data.
Results, observations, and conclusions:
We correlated MICP pore size measurements with grain size measurements and used the correlation to optimize a resistivity-based grain size-to-pore size transform. We next determined an algorithm to compute grain size from the gamma ray log and used this algorithm to determine grain size and pore size directly from wireline or LWD data. We used the resulting pore sizes to calculate the effect on methane solubility in Nankai Trough sediments. We found equilibrium temperature depressions of roughly 3-5 degrees C and solubility increases of 20-25%.
Significance of subject matter:
This work is significant in that it allows us to better assess the distribution of methane hydrates in Nankai Trough sediments, which in turn will allow more effective and efficient methane production from hydrates in this area. Further, this work provides a method of determining phase equilibrium behavior from log data, which provides valuable information for hydrate exploration and production in the Nankai Trough and other potential methane hydrate plays around the world.
Coalbed methane has become a viable resource for meeting the needs of natural gas consumption. Many projects were started in 1991 to take advantage of tax credits offered by FERC. These projects have had to carry on beyond the tax credit. One such is Belden & Blake/Devon Resource's Blacklick Project. The Blacklick Project was started by O'Brien Methane Production as an attempt to cash in on tax credits. O'Brien drilled twenty wells but only six were treated before the project was sold in late 1992 to Devon Resources Inc. and Belden & Blake Corporation partnership. The remaining initial wells were frac'd over the course of the next two years. The overall results were not stellar. Water production exceeded expectations, while gas production had not followed the "typical" incline experienced at other CBM Project areas. In late 1995, Belden & Blake shifted responsibility for the Project from the Corporate Office to the satellite office at Pleasantville. At this time a complete review of the Geology and Operations was under taken. The results of this review spurred a new round of drilling. This drilling utilized the geology to pick optimum areas. The short falls discovered in the operational review were also tested. The 1996 CBM program for Blacklick exceeded the expectations of all involved. The process used to improve this project area required cooperation of Engineers, Geologists and Field Personnel. It also utilized a fair share of practical experience of pumping operations learned in shallow oil production.
The Blacklick Project is a conventionally operated CBM Field containing fifty-five (55) wells (Figure 1). This field is officially known as the Blairsville and Campbells Mill Pools. Located in the Northern Appalachian Basin, this is the only CBM field in south central Indiana County, Pennsylvania (Figure 2). The field sits astride the trough of the Latrobe Syncline and is flanked to the east by Chestnut Ridge Anticline. Gas is produced from several conventional reservoirs in this area and an extensive pipeline network exists. The tax credits for unconventional reservoirs set up by FERC spurred an attempt by O'Brien Methane to locate and develop a CBM Project in the Northern Appalachian Basin. The Blacklick Area was chosen for the thickness of virgin coal and the poor roof conditions in the mined out area north of Blacklick Creek (Helen Mine). O'Brien drilled 20 (twenty) wells in late 1991 and early 1992. Six of these were treated using a myriad of completion techniques. These initial wells encountered significant quantities of coal (200 inches average total), but water and gas production was a mystery. Gas open flows exceeded 100 MCF/D, but on-line performance was much lower. Water production never showed any signs of decrease. In late 1992, O'Brien sold this project to a Devon Resources/Belden & Blake Partnership.
Throughout 1993 and 1994, the partnership treated the remaining O'Brien wells and tied everything together with a gathering system for water and gas. Compression was also installed to maximize production. Field wide production averaged 500 MCF/D and 150 BW/D/Well. This was not considered economic. A complete review of the project was initiated in late 1995. All aspects of the existing wells were to be scrutinized. Geology became the first "target" for the inquisition. Several issues cropped up after this review. Engineering proved enlightening also. Initiated at this time was an external review and feasibility study of open hole completion techniques including the highly successful cavitation type completion. In 1996, the partnership proceeded with a six well drilling program based, in part, on the internal review of the field.
Gao, Wenkai (Drilling Research Institute of CNPC) | Dou, Xiurong (Drilling Research Institute of CNPC) | Sheng, Limin (Drilling Research Institute of CNPC) | Liu, Yongfeng (Research Institute of BHDC)
In a cluster and horizontal coalbed methane well drilling environment, one of the most effective methods to enhance the individual well producing rate is to prevent the bit drilling out of the seam top and floor, and the bit is always in the best position to extend along the target layer. The conventional electromagnetic resistivity or gamma measurement while drilling system mounts far away from the bit(more than 7m), however the ROP of CBM drilling is usually high, which lead to time lag and large deviation of trajectory. The use of near-bit and surface vibration measurement while drilling system can identify the seam top or floor as quickly as the bit contact the boundary, to increase drilling efficiency. The paper briefly introduced the work principles, composition and application of the system. The system is composed of near-bit vibration measurement tool, surface vibration detecting device, wireless transmitting system, signal processing and indicating software system. The downhole measurement system detects and processes the near-bit data, the result is sent to surface in real time, then operators can change drilling parameters in time if harmful downhole conditions are indicated, considering with the surface measurement. This system has been extensively tested and proved to be effective in identifying the difference of breaking fossil coal and other rocks. Detail of the test and the method to deal with the data will be discussed in the paper. Quickly identifying the coalbed boundary due to vibration detected both downhole and surface allows operators to take timely remedial action before the bit drills out of seam layer. Thus the drilling efficiency has been remarkably improved.
Abstract This paper presents the results of a preliminary investigation of the coalbed methane potential of the Zonguldak Basin in Turkey. A stochastic approach is used in the investigation primarily because of the lack of sufficient data. The results clearly indicate the adequacy and the advantage of the stochastic approach over the deterministic procedures. The Monte Carlo simulation is used to obtain the probability distribution of in-situ and recoverable coalbed methane reserves in the Zonguldak Basin. An economic evaluation of a potential development project is also presented. It is shown that despite the conservative estimates of the reserves, coal bed methane production from the Zonguldak Basin is a feasible project. P. 227
A case study is presented to highlight potential problems with sampling gases from conventional coalbed cores taken from two wells in the Lower Saxony Basin, Germany. Cores were placed in canisters at surface shortly after extraction from the subsurface and desorbed at reservoir temperature. Gas samples were collected intermittently during the testing using Tedlar© PVF bags (Tedlar) in one well and using glass vials in the other. Gas samples from both wells were analyzed for elemental composition using a gas chromatograph-flame ionization detector (GCFID) system and gas isotopic composition using a gas chromatography-mass spectrometer (GCMS). Results of the GCFID testing from the first well indicated a very high degree of atmospheric contamination in comparison to samples from the second well. GCMS testing of the gas samples from the first well indicated near-impossible isotopic compositions compared to the samples collected from the second well.
Issues were observed with using Tedlar sample bags for gas sampling from the first well, manifested through the apparent levels of atmospheric contamination and strange isotopic composition results. Extended residency time of gas samples within the Tedlar bags allowed coal gases to diffuse out of the bags and atmospheric gases to permeate the sample bags at different rates, resulting in contaminated samples. This behavior was not observed in the second well—in which samples were stored in glass vials prior to analysis—and reflects the effectively impermeable nature of the glass sample vessels. The result has been too low methane (CH4) concentration to perform reliable isotopic analysis from samples stored in Tedlar bags. From the dataset constructed from the two wells, changes to operational procedures in the collection, storage and analysis of canister gas samples were made.