Abstract

This paper describes the application of hydraulic fracturing to a laminated sand/shale sequence. The stimulated zone, the Telisa Formation, is productive in several fields located near the large Duri Field in central Sumatra. The largest Telisa accumulation occurs in the Balam South Field in an anticlinal structure covering 3430 acres with an average gross thickness of 120 feet. The formation is a sequence of interbedded sands, silts, and shales, with individual bed thicknesses from just a few inches to several feet. Telisa production from this field began 19 years ago. However, recovery has been low (less than 2% of original oil-in-place) due to low well productivities and limited well development. The average unstimulated well produces 100 BOPD with an average watercut of 7%. Several attempts were made to increase productivities by varying drilling and completion techniques (oil based mud, high density perforating, open hole completions). When these were unsuccessful, fracturing was considered. The two key factors in favor of fracturing were the large oil target and near original pressure gradient. The three main concerns were: predicting post-stimulation productivities with uncertain permeability distribution, containing fracture height growth, and preventing premature screenouts from a suspected narrowing of the induced fracture width in the higher permeability lenses. A two stage fracture treatment was designed to place proppant across the entire zone. Well response during placement indicated the induced fracture of the second stage does not intersect the induced fracture of the first stage. Post-stimulation analysis suggests limited height growth outside the zone. A total of 13 Balam South wells have been fractured to date. The average production per well increased from 62 BOPD to an initial rate of 318 BOPD and a sustained rate of 233 BOPD (a four-fold increase). Fracturing the Telisa Formation in one other field has proven equally successful and is planned for additional fields.