Impact of Compressibility Change due to Overpressure on HC Volume on Karachaganak Gas Condensate Field

Inappropriate surface infrastructure sizing due to overestimation of initial reserves may lead to financial losses for a company. One of the many reasons why surface facilities are inappropriately sized is due to lack of subsurface understanding, misinterpretation or lack of data [1]. The current work is dedicated to give more understanding on possible expected behavior of the Karachaganak field based on hard data and its implications on hydrocarbons in place. The Karachaganak gas condensate field is 20% overpressured reservoir. Current production is mainly focused on oil rim. Gas production is delayed to later times, as a blow down process. Based on real cases in the past for overpressured gas reservoirs there was developed a special material balance equation where it assumes different compressibility for a reservoir before and after reaching hydrostatic pressure. There are two main theories that explain the causes of overpressured reservoir material balance calculations [2]. Rock collapse theoryShale water influx theory The Karachaganak field is a carbonate field with negligible amount of shale which excludes the shale water influx theory. Repeated well test data measured on the same well during a different period of the well life clearly show how rock collapse theory works in the field thus supporting the first theory occurrence on the field. Based on the current simulation model with implementation of changing compressibility to reflect pore collapse, authors provide calculations and its impact on original oil and gas in place volumes.