TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents results related to the use of the ball sealer diversion technique to fracture long and multiple Triassic sand intervals in the Alwyn Field. It also focuses on the methodology adopted to design and prepare the treatment. This technique was applied on a well producing from a gross pay zone thickness of 350 m with a perforated length of 98 meters. The production decreased drastically after condensate deposition in all reservoir intervals induced high skin levels. Due to low permeability, matrix treatments were discarded as a solution. Instead, a proppant fracture treatment was planned to by-pass the skin, using ball sealer diversion to treat the entire perforated interval.The treatment was performed successfully in several stages including gel pad, proppant and ball sealers. Good indications of diversion showed that most of the intervals were fractured. However, performing such a treatment requires sophisticated engineering to determine the optimum number of stages, number of ball sealers per stage, gel and proppant volumes per stage and pumping rate. The success of this operation will allow the technique to be considered for wider application such as fracturing long intervals in deviated or horizontal perforated wells at moderate cost.

Development of the Tin Fouye Tabankort Gas Field, located approximately 600 miles South-Southeast of Algiers, was initiated in 1996 with the simultaneous start-up of surface facilities construction, workovers of existing wells and drilling of new wells, The evaluation of hydraulic fracturing operations was an important step in the formulation of the optimal development strategy for this complex Ordovician age sandstone reservoir. However, production performance and hydraulic fracturing design were uncertain due to large reservoir uncertainties (heterogeneity's, kh, skin, presence of natural fissures, etc.) and doubts about the fracture height growth behaviour. To overcome these uncertainties, a complete set of measurements were performed including pre and post- hydraulic fracturing well tests, minifracturing on all wells including some bottom-hole pressure recording, temperature logs, and radioactive isotope tracing in both gel and proppant. Analysis of the collected data allowed a better understanding of reservoir characteristics, the influence of natural fissures on fracture design, and fracture growth behaviour. Indeed, results showed that the radioactive shale immediately above the IV-3 reservoir was often not a barrier to fracture growth. With this knowledge, perforation and hydraulic fracturing strategies were steadily improved to maximize post-job production, and optimize project economics, Results proved to be very successful with the average production increasing by a factor of 5 at significantly reduced drawdown pressures. P. 361