Abstract
This paper will cover the design and installation of BP’s first 15Kpsi Open Hole (OH) completion in the Sultanate of Oman in March 2016 and also the initial execution results of the stimulation treatments in July/August of the same year. This change to the current well design and execution strategy has become necessary due to variable cased hole horizontal well results and greater understanding of the challenges of delivering efficient and sustained gas production from the higher fracture gradient areas of the Barik reservoir.
The Khazzan (Barik) development in the Sultanate of Oman operated by BP is a tight gas project, requiring hydraulic fracturing of tight gas resources. Tight gas production from the deep hot reservoirs in the Sultanate of Oman has historically concentrated on cased hole completions stimulated with large hydraulic fractures. The original Basis of Design for Khazzan for Full Field Development consisted of horizontal wells with multiple hydraulic fracturing stages performed within a Cased & Perforated 4-1/2″ liner design. Challenges encountered with the CH approach have included the following:
Tight pressure deployment/pumping window within the existing completion design, complicated by a wide variation in areal and vertical stress regime.
Variability in the injection response, proppant placement and particularly the quality of the fracture/wellbore connection that would and has been achieved.
Lack of predictability regarding post-frac production rate, due to a variation in fracture placement achieved due to above two reasons.
In 2014 a decision was made to introduce some flexibility in evaluating suitable fracturing designs incorporating a number of Lower Completion (LC) styles, one of which was a horizontal open-hole completion. Optimizing stimulation performance by evaluating ball dropped activated systems and over-displacement was seen to have significant potential. A multi-disciplinary approach involving drilling, completion, stimulation, intervention and subsurface was performed to ensure Project value was maximized and the objectives delivered.
This paper will cover how the pressure rating of the OH completion was designed to 15 kpsi, in excess of the existing CH pressure rating. This includes screening and evaluation of the available open-hole LC system design and operational characteristics suitable to deliver propped gel fractures in 6″ OH for 1,000 m horizontal wells. Screening criteria included; system/equipment technology status, associated drilling requirements and design for "5-7/8″ hole" cost and duration versus the existing 8-3/8″ hole configuration and an ability to meet the well stimulation Statement of Requirements (e.g. fracture placement, zonal isolation).
The final system design will be detailed including wellbore orientation and trajectory, hole and casing sizes, zonal access and isolation method(s) and hydraulic fracture parameters, including fracture spacing, geometry and treatment design.
Operational results will be presented for well construction and stimulation phases. Well construction results will include drilling performance comparison, wellbore preparation for the completion installation, drill-in/completion fluid requirements and packer spacing/zone selection criteria. Stimulation execution results will include evaluation of execution versus design, comparison of stimulation results for ball drop stage results versus plug and perf results. Assessment of Radioactive (RA) tracer results and evidence for OH packer integrity will also be presented.
Conclusions will include an initial comparison of the execution of the drilling, completion and stimulation phases and lessons learned on the success of the design versus the original objectives.
