Uplifting the Profitability of a Mature Gas Giant in Pakistan Using Diminutive Sidetracks

Abstract

Abstract One of the key challenges for Oil and Gas industry in current (low price) scenario, is efficient handling of mature Assets. This is because of the fact that reasonable amount of hydrocarbons still exist in such reservoirs but in scattered and partially-drained locations. Moreover, lower production rates, combined with ever-increasing costs, hardly satisfies the economic screening criteria for their expansion with new wells. This study presents an approach used on such a Mature Gas Giant in Pakistan, in order to re-vitalize old wells and exploit the scattered sweet spots (still prevailing in reservoir), with the help of a robust engineering and geological strategy. The field under study was discovered in 1950s, in the eastern onshore area of Pakistan. The primary reservoir, under study, is a depletion drive fractured limestone i.e. no pressure support was observed in P/Z data. At present, more than 92% of the EUR has already been produced from this reservoir, which translates to 82% of Field In-Place volume. However, the performances of multiple wells have gone down with time, due to the depletion in Reservoir Pressure and the channeling of water towards producing wells-through the faulted/fractured zone. To cut water production and arrest the Annual field decline of 7-8 %, various activities have been carried out, including cementing, tubing size reductions, chemicals; but all the efforts went in vain. In this paper, a detailed approach is presented, that was taken to tap the undrained areas in the vicinity of the existing producers - suffering from water hold ups and low gas rate problems. The Production logs were used first to identify the water production zone. Afterwards, a comprehensive algorithm was developed to analyze the Geological and Geophysical parameters and identify the undrained prospects while keeping minimal capital exposure. So far, a gain of around 10 MMScfd have been observed with the help of two engineered Sidetracks - which has added around 10 - 15 BCF reserves in our portfolio. The most common issues encountered in a mature asset are liquid loading and water breakthrough. This study illustrates the methodology to resolve such issues with minimum investment towards the end of field life. It focuses on the benefits of sidetracks as a production enhancement tool, to reduce the annual decline. This paper offers an innovative approach, to utilize each geological and engineering data set in a systematic manner, in order to re-work old wells at optimum locations to evade issues affiliated with gas entrapment and water production. In the end, the paper also describes the evaluation process of production gains, geology, well construction, and completion types, that can be adapted to reap maximum rewards in such mature fields.