Gas Well Deliquification for Maximising Recovery from Mature Gas Assets

Abstract

Abstract VICO Indonesia operates the Sanga Sanga PSC in East Kalimantan which is on production since 1972. Reservoirs are mostly gas and depleted. Very Low Pressure compression "VLP" systems, which operate at 15–25 psig suction, are widely installed across all fields. As a result, flowing tubing head pressures in a large number of wells are in the order of 40 psi. Completion tubing sizes range from 2 3/8" to 4.5" with the majority being 3.5". Despite this, a large proportion of VICO's existing gas wells are subject to liquid loading, leading to premature abandonment of producing zones when the gas velocity in the tubing is lower than the critical velocity. This phenomenon is influenced by the tubing size, surface pressure and the amount of associated liquids produced with the gas. Historically, some temporary activities were carried out to overcome this problem. This included the reactivation of wells by flowing to flare and/or dropping foaming agents. The result of this type of "temporary" application was very variable and inconsistent. In an effort to continuously optimize the system and reduce the abandonment pressures, a large scope deliquification project was launched in 2006. The project included the application of capillary strings for down-hole chemical injection, plunger lifts, and wellhead compressors. This program was applied across all fields in VICO. The results were very positive in bringing back the production strings previously considered marginal or not producing. The field wide implementation program for both capillary string units and well head compressors was conceived to allow periodic relocation and optimization of the units and the system. As a result, all these deliquification techniques have now become a core element of the Base Production System. They continue to be optimized on a day to day basis and as a whole they are responsible for approximately 10% of the total production from VICO. Introduction VICO has been continuously producing the Sanga Sanga PSC in East Kalimantan since 1972. Its production is primarily gas, which accounts for approximately 80% of the total. Currently the majority of this production comes from very depleted reservoirs. The bottom hole reservoir pressures are mostly within the range of 2 to 3 ppg, hence low surface pressures are required to produce these reservoirs. Very low pressure (VLP) compression systems have been installed at plant station across all fields. The suction pressures of these VLP compressors are usually within the range of 15 to 25 psi, thus the flowing tubing head pressure of most wells flowing to these VLP systems are in the order of 40 psi. This very low pressure system has been successful in maintaining the wells producing for long periods of time. As time has passed, a large number of wells -even flowing to these VLP systems- started to suffer liquid loading problems. Liquid loading is usually influenced by the amount of liquids associated with the gas production, the tubing size, the surface pressure and, off course, the rate of production, which defines the velocity of both the gas and liquid inside the tubing. This problem has been a focus area for VICO since a significant proportion of the remaining reserves are located in some of these large depleted reservoirs. In order to overcome these problems, several deliquification techniques have been introduced and implemented since 2001. However, since no systematic approach was initially applied, the results of most of the initial efforts were very variable, and limited success was achieved. Subsequently, a larger and more systematic approach was applied after 2006. This program is still the one being applied today and it is the one responsible for keeping about 10% of the total production from VICO.