The objective is to achieve improved productivity from an unconventional fractured reservoir using uncemented liner completion over the standard cemented liner completion.
Exploration and production of an unconventional fractured Najmah & Sargelu (NJSR) reservoir in Jurassic section has been a challenging task due to the presence of challenging reservoir quality like tight fractured limestone, very low matrix porosity, uncertainty on natural fractures, high stress, etc. NJSR reservoirs are considered as a secondary target. As the deeper primary reservoir needs to be evaluated, testing of NJSR reservoir takes considerable time after drilling which lead to permanent plugging of NJSR fracture network by invaded oil based mud (OBM). Mixed success has been observed on sustainable production from NJSR exploration wells. Production from fractured reservoir relies primarily on intersecting interconnected natural fractures, optimal drilling and special completion technique. Protecting the natural fractures present in NJSR reservoir can increase the reservoir contact and production.
A study conducted on this reservoir suggested to target only NJSR formation and install uncemented liner to eliminate the damage caused by cement invasion and achieve sustainable production. The study also emphasized to activate the well as soon as possible after completion to revive fracture conductivity. Uncemented perforated liner completion method has been selected for field trail in an exploratory well to maintain borehole integrity and control production of solids, connecting open fractures, increase inflow area and enhance production.
The case study well targeting NJSR reservoir was drilled upto 14,925ft and 5" uncemented CRA liner was installed against reservoir section. The well was completed with permanent packer using 3-1/2" production tubing. Well fluid was displaced with diesel, mud clean solvent was spotted inside 5" production liner and the uncemented liner section was perforated using wire line guns in underbalanced condition. The well became active after perforation and flowed naturally oil and gas with 1.8% H2S.
A successful implementation of uncemented liner completion technique in an exploratory well for the first time proved to be effective in fractured reservoir compared to the conventional cemented liner completion. Application of uncemented liner completion technique has preserved fracture connectivity, eliminated formation damage due to cement invasion and reduced time and cost of cementing and stimulation. During initial testing the first field trial well has produced oil and gas without stimulation, which is a success compared to conventional method.
As a final recommendation from the study, future exploratory wells targeting NJSR reservoir will be drilled in high angle trajectory and completed using uncemented slotted liner with swell packers to improve the productivity.
This paper will discuss in details on new completion strategy, testing of deep HPHT well and performance of first exploratory well completed with uncemented liner.