How to Revive Mature Oilfield Production from Surface Aspect, Case Study: Venting System to Gas Scrubber Project in XBU Fields

摘要

XBU is an offshore mature oil fields area which has been produced more than 40 years. There are three fields as main producers from this area; they are CC, RR, and WW. Reservoir pressure in the main reservoirs were originally more than 1700 psi, and by the time it was decreasing to 300 - 500 psi, so many wells in XBU could not be produced due to gas problem and low influx. In the well which had reservoir pressure below bubble point, in every drawdown of ESP, the gas would release in fill the column of annulus in the wellbore. If the casing pressure is close or flow to the system riser pressure of the platform, the column of gas would push the fluid level in the wellbore and make problem of the pump (gas lock, pump off, slug flow, etc). Production operation and engineers then came up with a solution of modification in the surface production facilities by installing venting system through scrubber in the platform which has gas problem wells. By venting the casing pressure to the scrubber and vented to the atmosphere, the production of each well was stable and ESP runlife was longer. This equipment also needs to pass QHSE requirement since almost all of them were located in the unmanned platform. Preliminary study of this project came from several finding of gas problem in almost all XBU wells. Short ESP Runlife also caused by this problem. Design of venting system though scrubber was created by the team with some constrain and must meet safety and technical requirement. Installations of the design were widely applied in year 2008 to 2009. The basic principle of this technology was to make fluid column in the casing as big as possible, so the maximum fluid level can be drawdown by ESP. It can be indicated by having casing pressure as low as possible and increasing flowing bottomhole pressure. This method proved can maintain the decline rate of XBU oil production from 2008 to 2017. Better ESP runlife for problem wells due to gas also can be a parameter of the venting installation success. NWA B-07 and SWW A-03 wells which previously shut in and could not be produced due to categorized as gassy well were an example for proving the methods, those well can be back online after installing venting system through scrubber. This paper will elaborate the general problem of offshore mature oil fields both sandstone and limestone, especially the depleted reservoir which has gas problem. Installing gas venting system through scrubber proved can maintain oil production for about 10 years and even more.