Development of water production type curves for horizontal wells in coalbed methane reservoirs.

摘要

Coalbed methane is an unconventional gas resource that consists of methane production from the coal seams. The key parameters for the evaluation of coalbed methane (CBM) prospects are the gas resources, reserves and deliverability. Coalbed methane reservoirs are dual-porosity media where the vast majority of the gas is stored in the low permeability coal matrix (primary porosity) by sorption. The flow to production wells, however, occurs through the coal's natural fracture system (secondary porosity), which stores relatively small amounts of gas, because coal matrix practically has no permeability.; For the gas to be released from the coal, its partial pressure must be reduced, and this is done by removing water from the coalbed fractures. During the dewatering process, the gas desorbs from the coal matrix, thereby gas rate increases and the water saturation decreases. The water production declines rapidly until the gas rate attains a peak value and water saturation approaches the irreducible water saturation i.e., reaches connate water saturation. Once the peak gas rate is attained, CBM reservoirs act like a conventional reservoir. Reservoir engineers usually use production decline curves in order to predict well performance.; Since the behavior of CBM reservoirs are complex when compared to conventional reservoir, the use of a numeric simulator is the best way to predict the CBM production behavior. Operating a simulator requires in-depth knowledge and detailed data to get accurate results. They are also expensive to small producers. Considering these factors, using a simulator might not be the best option. Hence, in order to develop a simple and yet a reliable to tool to forecast the production in a CBM reservoir with good accuracy, it was taken upon to develop type curves for both gas and water production.; The objective of this study was to develop a simple and reliable tool was developed to help with water production predictions in horizontal coalbed methane wells that are located in the (Northern Appalachian Basin). Upon development of a unique set of type curves, independent producers will be able to evaluate the future production of water from the wells. A correlation for the peak water rate was also developed in order to forecast production if no production data is available.