The Application of Surveillance on Gas Wells to Prevent Shortfall in Zona 13 Donggi-Matindok Field

Abstract

Gas well production is governed by Gas Sales Agreement (GSA) which is consist of 3 main parts, i.e.: volume, duration, and price of the gas. If seller fail to fulfil all clause stated on the GSA, several punishments will be conducted. One of the clauses related to gas sales volume, in which if gas delivered to the buyer for 1 year is less than the amount stated in GSA, buyer need only pay for 75% gas price for the next year. Several surveillances need to be done to prevent it.

Modified Isochronal Test (MIT) is an enhancement of isochronal test. This method proven more feasible to be done because we don’t need to wait for reservoir pressure reach the initial to proceed to the next choke step. We change the phase of produce-shut in wells process several times. By giving disturbance in the wells, we could see pressure change in which the data could be used to approach permeability value, skin, absolute open flow (AOF), and the estimation of reservoir boundary. All those data then used to approximate deliverability of the wells. MIT, conducted in 2019, indicated that damage value smaller than the last measurement (2018). we can see from the derivative pressure plot that boundary is not existing. Overall measurement indicated that optimistically Donggi can supply the amount of gas volume stated in GSA. This conclusion is corresponding with the production of Donggi-Matindok still stable until now. Pressure drop is also relatively small since initial production (± 300 Psi). MIT is reliable and feasible tools to see deliverability of gas wells. Meanwhile, we also need to see the condition of reservoir  horoughly. First, we need to see the movement of Gas-Water Contact (GWC). We use Reservoir Monitoring Tool (RMT) to compare the result with RMT at initial condition (during open-hole period). Second, we use Pressure Build Up (PBU) to get more information about reservoir boundary condition. PBU provide a description of reservoir condition several feet from the wellbore by interpreting pressure behavior. This test covers more range than RMT. And the last data is generated from Mobile Test Unit (MTU). This is typical test unit but conducted near the wellhead to get more accurate data than measuring in Central Processing Plant (CPP). By combining those four data, we can get an approximation of gas-rate range to be produced and get a stable gas well performance to supply buyer’s demand based on GSA.

We live in a paradigm, that oil and gas industry is only focused in producing oil. We should change this paradigm because gas production also gives promising profit. Efforts to develop gas well should be done in the same pace as we develop oil well.