The Telisa Formation is a thick shale interval with minor shaly sand reservoir in the Central Sumatra Area. This sand in Bangko field has not been widely developed because’ most of the existing producers are completed in the deeper formation, such as the planned Dun 1600′ sand for Waterflood and 1680′, 1710′, 1740′ sand Waterflood Expansion Phase 1 and 2. Therefore, it is difficult to recomplete the Telisa sand.
This shalysands and thinly laminated sand-shale sequences resulted in a reservoir with low permeability and poor connectivity, which hinder a reasonable primary recovery. Detailed reservoir characterization will capture the reservoir heterogeneity and ultimately will improve oil recovery. The level of work included core descriptions, formation evaluation adjusted with core properties obtained from laboratory measurements, detailed seismic interpretation and attributes analysis, like acoustic impedance, seismic .frequency and phase.
Model building for shalysands zone using a variety of wireline measurements recorded at different times can seem like a formidable task. However, this task becomes easier with some basic knowledge about wireline measurements and their role in the final solution of estimating the reservoir quality. Using a gradient field NMR tool operated with a 2 ms pulse-echo timing, have indicated that a porosity related to clay mineral content is not identified previously. This implies that the NMR tool may provide a direct determination of the pore volume controlling the cation exchange capacity (CEC) effects. The efforts have resulted in a self supporting resistivity interpretation method that brings a new level of confidence in determining the water saturation from shalysand resistivity logs.
The Imaging Tool data from seven wells were also used to determine fracture orientation, stress and strain system across the Telisa Formation to identify the optimum direction of frac-job, which is usually perpendicular with maximum stress. This tool also provided detail sedimentary structure for environment analysis and high resolution resistivity for detail sand-shale layers identification.
Five hydraulic frac-job have been performed at Bangko field to date, which four of them were successful. The incremental production of those successful jobs for one month has paid the cost for the frac-job itself
The study of this shalysands. in Bangko field is an excellent opportunity to : (1) demonstrate the economic importance of these zones, (2) understand the methodologies required for identifying and evaluating these pay types and (3) help the company to find additional reserves in the Central Sumatra basin.
Authors : Andry Nabasir, Andriyanti S, Hendar SM, Haruji MP & Subagio