Change Of BOE Conversion Factor with Reservoir Pressure Depletion - A Case Study Of XYZ Field

Abstract

The objective of this paper is to investigate the impact of BOEs (Barrel of Oil Equivalent) conversion factor for Gas and LPG with reservoir pressure depletion on production and reserves figures with reference to Petroleum Resources Management System (PRMS) guidelines. In general, it is a common practice of E&P (Exploration & Production) companies to use same BOEs conversion factor for Gas (especially wellhead) and LPG throughout the life of reservoir. However it is understood that Gas and LPG composition plays a vital role on conversion factors of BOEs used which has an impact on the wellhead production figures, well head reserves booking, field economical limit and etc. In this paper, "XYZ" field is considered to evaluate the impact of BOE conversion factor on wellhead gas and LPG. The "XYZ" field is producing gas condensate from HPHT (High Pressure & High Temperature) fractured carbonate and clastic reservoirs in upper Indus basin of Pakistan. The field was discovered in early 1990’s and produced ~ 70 BSCF of gas till to-date. The standard BOE gas conversion factor for "XYZ" field is 5.80 MSCF/STB which gives 1,224 BOEPD on current production data and expected remaining recovery of around 40 MMBOE. The recent BOE conversion factor based on current gas analysis is found to be 4.46 MSCF/STB that translates 1,500 BOEPD and expected remaining recovery of 46 MMBOE based on average reservoir wise BOE conversion factor of 5.13 MSCF/STB. LPG is based on 70% propane & 30% butane, therefore its fixed composition restrict us to use a BOE conversion factor in the range of 11.60 to 11.84 MT/D. BOE estimation and results in this paper conclude that the change of BOE factor depend upon the change in gas composition with production history at wellhead and depletion in reservoir pressure. Based on this working, wellhead production figures, well head reserves booking and etc for XYZ field have been revised. This also dictates the importance of booking these figures at sale condition.