Design Evolution of Complex Oriented Perforating System in Highly Deviated IWAG Well with Fiber Optics
Authors: Oka Fabian , Orient Samuel , Farhan Suratman , Hazim Kamarulzaman , Haydn Brendt Sinanan , Sylvia Mavis Ak , Tomaso Ceccarelli , Supakit Rugsapon , Jennie Chin Pui , Maisara Arsat 
Published: November 2020

B Field Overview and Background

Located in the South China Sea, B oil field was first discovered in 1971 and has been in production since 1982; it is located in offshore of Sarawak, Malaysia, with a water depth of approximately 70 metres. The field has an interval of over 7000 ft. of stacked reservoir sands and thin continuous shale layers, making up approximately 165 individual reservoir units with Late Miocene to Early Pliocene in age, with the stratigraphic intervals reservoir section.

With the objective to find a technically and economically viable enhanced oil recovery (EOR) development concept for B oil field, a feasibility study was conducted by taking several EOR strategies into considerations – low-salinity waterflood, chemical EOR, and immiscible water alternating gas (IWAG). By evaluating individual layers of the field, the study concluded with a recommendation to implement EOR via IWAG on EF reservoirs on the basis of value, timeline, and flexibility for future EORs; IWAG would yield the best result from technical and economical point of view, and also with the ability to be implemented as earliest as possible.

The theory behind IWAG implementation in the field is that the gas component of IWAG injection will help to sweep oil that is left along the top of reservoir sands due to poor water-oil mobility ratio and gravity effects, and due to the fact that gas moves quickly in the reservoir, the water component of IWAG injection will come into assistance by controlling gas mobility and maintaining reservoir pressure as more drainage points are introduced into the reservoir. Additionally, water injection provides the control to improve the aquifer's sweep, three-phase hysteresis effects and reduced residual oil (in gas) is expected to improve recovery mobilizing more oil in the reservoir, and gas injection may also assist to drain oil that are trapped in attic accumulations. In B field, IWAG injection involves gas and water injections into wells that are located down-dip of the reservoir.

Out of four IWAG injector wells in the recent B field drilling campaign, one well was selected to be equipped with a Distributed Temperature Sensing (DTS) system after considering the following benefits that the DTS system would provide:

Conformance monitoring specifically for water to qualitatively identify which sand the water is being injected to or any potential internal crossflow Quantitative flow into each reservoir layer derived from warm-back analysis for the short term and hot-slug propagation for the long term instead of running wireline production logging tool (PLT) Hydraulic fracturing profiling to prevent the formation from fracturing unintentionally due to the water hammer effect or cooling of formation with injection water (i.e., thermal fracture); inversely, when zonal fracturing is intentional and required, profiling to gauge effectiveness and fracture spread Real-time injection issues or zonal anomaly identification to eliminate the need to perform well intervention to obtain information which often results in delayed action Injected gas or water fluid front monitoring when combined with existing DTS in producer wells Reduced intervention risks in a highly deviated well that could lead to fish in hole and potential workover