Production Strategy Calls for Injection of High-Gas/Oil-Ratio HP/HT Crude

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 203484, “The Innovative Production Enhancement Strategy of Using High-GOR Crude in HP/HT Reservoir To Lift Upper Reservoir Production, Case Study in Iraq,” by Xueqing Tang and Zhongliang Cheng, SPE, PetroChina, and Ruifeng Wang, SPE, CNPC, et al. The paper has not been peer reviewed. Halfaya oilfield in Iraq contains multiple vertically stacked reservoirs. The main oil reservoirs are under primary development at the time of writing. The remaining deepest high-gas/oil-ratio (GOR), high-pressure/high-temperature (HP/HT) carbonate reservoir, with an original pressure gradient of 0.867 psi/ft, has been drilled and tested but not yet developed. A production strategy has been proposed in which high-GOR crude can be injected into the upper oil reservoirs with partial pressure depletion as an energy-conservation measure in view of its high wellhead pressure and good productivity during drillstem tests (DST), thereby achieving production enhancement and synergy among reservoirs. Introduction The Halfaya field is a supergiant hydrocarbon accumulation in southeastern Iraq. Structurally, it is a gentle elongated anticline trending northwest/southeast. It is 20–22 miles long and 5.0–5.9 miles wide. It features nine vertically stacked reservoirs, including two sandstone reservoirs with high permeability and seven highly heterogeneous carbonate reservoirs (including Sadi B, Middle Cretaceous Mishrif, and Lower Cretaseous Yamama). The main reservoirs, Mishrif, Nahr Umr, and Upper Kirkuk, contain edge water and bottomwater support. Early field production began in April 2005. So far, 313 wells have been producing and the field has successfully achieved 413,000 BOPD compared with the plateau production target of 400,000 BOPD, with a water cut of 8.7%, producing a GOR of 759 scf/STB.