Optimizing gas production in the existing and new reservoir layer using a combination of compensated neutron log interpretation and selective perforation methods at PSU Field wells, North Sumatra

Abstract

PSU Field is one of the areas that are included in PT. Pertamina Hulu Rokan in North Sumatera. It produces gas and has continued to contribute to fulfill the gas demand for the local consumers, especially the industrial market. Based on the information on the decree issued by the Power and Mineral Resources Ministry of Indonesia, the local industries need 81 mmscfd of gas supply until 2024. Out of the total demand, PSU Field of PT Pertamina Hulu Rokan is allowed to supply 7 BBTUD (5,8 mmscfd). Therefore, in order to accomplish the desired gas volume, so PT. Pertamina Hulu Rokan has established some  working fields to produce gas: ARB Field and GBG Field.

Producing gas in each of the fields has its own challenges. ARB is challenging because of the increasing gas water contact in the subsurface layer that potentially could have contained hydrocarbons. This condition might have been caused by the incorrect production method which is to produce the well using the commingle layer that could intensify the water production and decrease the oil production. At the same time, GBG field’s challenge is the amount of reservoir layers which are thick and have been depleted (maximum recovery factor and decreased pressure). To overcome this challenge, prospecting was needed on the thin reservoir layers. Used methods to minimize the situation is by using a combination method of compensated neutron log interpretation and selective perforation. This method was applied both in ARB-01 and GBG-55 even though each has its different cases.

Case 1 (ARB-01 field) used the combined method of compensated neutron log interpretation and selective perforation and produced low-pressured gas and cumulatively 112.91 mmscf of gas (February 2020-June 2021). In the meantime, Case 2 (GBG-55 field) has produced gas in the new layers cumulatively 51.52 mmscf by using the same method (April-June 2021). The total revenue from both of the productions is USD 657,720 which is equal to IDR 9,295,556,760. This achievement has also increased the gas well intervention success ratio on the PSU Field workplan by 100% (PPJ-38, PPJ-54, GBG-55, PPJ-60 and ARB-01).

By combining both methods, the problems related to contact fluid change and depleted reservoirs can be prevented in order to optimize the gas production and increase the company’s revenue in the midst of the instability of oil price.