Tight Gas Reservoir (TGR) - In Place Reserves Estimation and Economic Feasibility of Project

摘要

With the rapidly declining conventional gas reservoirs, Pakistan has been facing a severe energy crisis and it has become very important to look forward towards the unconventional resources such as tight gas reservoirs to meet the growing energy demands. Companies are looking forward for economically viable production from tight gas resources while considering new Tight Gas Policy of the country. The most important step is to correctly estimate Original Gas in Place (OGIP) and Estimated Ultimate Recovery (EUR) in case of tight gas reservoir before declaring the reservoir to be economical or uneconomical on the basis of detailed simulation and economic modeling. Techniques to estimate OGIP and EUR are different from conventional techniques since conventional techniques can lead to erroneous results. Flowing material balance is one of the methods which uses stabilized flowing pressure-rate data to estimate OGIP and EUR in case of tight gas reservoirs. Blasin- game Type Curve, Super Hyperbolic Decline (assuming b>1) and mathematical model based Power Law proves to be more accurate in case of tight gas reservoirs as compared to conventional techniques like, Arp’s Decline Curve, conventional material balance, etc. Paper presents practical application of above methods on the anonymous field data. Results from above methods are also validated from numerical reservoir simulation model. Economic model is made using Tight Gas Policy applicable in Pakistan and from sector modeling results, value of post-tax NPV is estimated for different cases to see whether development of tight gas reservoir is economically feasible or not. Super hyperbolic decline over predicts the reserves while Power law, flowing material balance and production type curves are most suitable for OGIP or EUR estimation of tight gas reservoir. OGIP and EUR of tight gas reservoir from these methods are approximately 7Bscf and 5.5Bscf respectively. Different cases were performed on a sector model of tight gas reservoir to optimize post-tax NPV. Most of the cases were not economically feasible but horizontal well having lateral of 570ft, multifrac (9 frac) having fracture half-length equals 222.5ft and fracture width equals 0.02ft is economically feasible due to maximum post-tax NPV and IRR value. It is recommended to use above mentioned methods for in place or EUR estimation in case of tight gas reservoir to avoid erroneous results. Along with that, tight gas reservoirs are economically feasible to produce in Pakistan with improved technology and by utilizing the incentives given by Government in new Tight Gas Policy.