A Paradigm Shift in Testing and Completion of Deep HPHT Exploration Wells - Polished Bore Receptacle (PBR) Improves Results and Operational Flexibility

Abstract

Abstract This paper presents an optimized engineering approach of testing and completing deep HPHT Jurassic wells using Polished Bore Receptacle (PBR). Also this paper describes how PBR assembly is applied in HPHT deep Jurassic wells. The Jurassic reservoirs in Kuwait are very tight formation with HPHT conditions containing sour light oil, gas and condensate. Due to high contrast in formation pressure profiles within 3,500 feet section, separate casings has to be installed for isolating three different formations. This requirement results in a well construction with tapered production casing (7-5/8" casing with a 5" liner below). The main producing Jurassic formations are carbonates with the presence of natural fractures. During drilling and work-over operations Oil Based Mud (OBM) with a density ranging from 15–20ppg is being used as drilling/kill fluid. Due to deep invasion of mud into the fractured carbonate reservoir, the wells are activated and stimulated using coiled tubing. Well intervention operations like perforating, PLT, bottom-hole sampling are vital during well testing and during life of the well. In deep wells with slim hole usually a packer assembly (or) Polished Bore Receptacle (PBR) is used for Testing and completion. In comparison the PBR seal assembly not only provides annulus-tubing isolation without the use of additional equipment but also offers room for tubing movement which is predominant in deep wells due to wide temperature variations. The simplicity of operation (sting-in/out) and achieving annulus isolation established additional merits for PBR in comparison with other conventional testing / completion strings. Overall, this methodology has delivered better operational capabilities by providing more clearance during through tubing operations and also increased flow area compared to conventional method of using a tapered string for Drill Stem Testing (DST)/Completion inside5" Liner. Introduction KOC is actively involved in search of finding light oil and gas from deeper reservoirs. These deep resersvoirs are spread in North, south and West fields in the state of Kuwait. The deep reservoirs located in the North Kuwait Fields are relatively deeper than the reservoirs in the West and south Kuwait Fields. The area is structurally very complex with NW-SE and NESW trending faults that tend to create different compartments. Also this complexity resulted in big contrast in the stratigraphic pressure profile. Due to this high contrast in formations pressures profile, a typical casing program is required to minimize the drilling problems and reach our targets safely. Where within 3,500 feet of drilling section, separate casings have to be installed for isolating three different pressure regimes resulting in a well construction with tapered production casing (7-5/8" casing with a 5" liner below). As per the existing casing policy, 2 to 3 zones are falling in 6" slim-hole section. The test zones in the 6" slim-hole section are being tested either with a packer or PBR Seal assembly in order to have tubing /annulus isolation.