Formation damage due to fines migration after the onset of water production presents a major technical challenge for many sandstone reservoirs around the globe. Oftentimes, significant productivity impairment is observed shortly after water breakthrough. This is particularly true for the Chad Doba basin lower "M" and "A" Sand reservoirs where studies have shown that a major contributor to this damage mechanism is the fluid velocity near the wellbore. As a result, exponential decline in productivity index is typically observed over very short periods.To arrest the productivity impairment, various completion techniques were evaluated for ways to reduce the velocity of the produced fluids near the borehole. Typical completion designs employed to date have been cased hole gravel packs (including frac-packs) which enhances the velocity profile of the well as produced fluids converge to the perforations. Maximizing the reservoir to the wellbore interface reduces the velocity profile and conceptually prolongs the onset of formation damage caused by fines migration. Based on that conceptual model, openhole completion techniques were evaluated for feasibility. Upon analyzing the geology of the selected candidate, it became apparent that fracturing the formation was possible as it was a relatively thin amalgamated sand package. As a result, the openhole frac-pack concept became a practical option as it results in the lowest velocity completion possible by maximizing the reservoir surface flow area.Openhole frac-pack completion activities were executed in mid-2009 and well productivity has been sustained even after water breakthrough. This paper reviews initial openhole frac-pack design concepts, execution lessons learned, and well productivity performance. Doba

The fields operated by Esso Exploration and Production Chad Inc. (EEPCI) in a consortium project with PETRONAS and Chevron in Central Africa, target highly unconsolidated sandstone formations. Sand control equipment must be utilized to prevent production of sand resulting in failure of downhole and surface equipment. Screens can erode as a result of "hot spots" where fluid velocities have increased considerably, allowing sand entry into the wellbore causing the subsurface equipment to fail and decrease production. With high drilling costs, and the limited amount of surface space, it has become critical to repair the more prolific of these damaged wells. This paper provides an overview of the development and utilization of various failed sand control equipment removal and replacement techniques for workovers. Screen removal poses challenges not typically encountered when pulling other bottom hole assemblies from the well. The team has utilized existing available equipment and modified tools to address these unique challenges during workover operations. Initial attempts to pull sand control equipment required weeks of rig time and met with limited success. Packer release tools were not always effective, and milling over these packers proved problematic. Additionally, long screen sections were difficult to pull. Learnings from each workover operation were incorporated until the optimum methods were eventually identified. Also, tools were modified resulting in time and cost efficiencies. Additionally, a systematic approach of selecting the best candidates for repair was developed, taking into account various wellbore complexities such as age, type of completion, length of the bottom hole assembly, among others. Each complexity is weighted based on previous pulling experiences as well as taking into consideration the total volume of oil to return to production. Since June 2009, 15 gravel pack failures were repaired, and wells returned to production utilizing these evolving and improving techniques. This represents over 5,300' of pulled screens. The first successful repair (June, 2009) required 20 days to complete. Applying learnings and improved techniques, the average repair time has decreased to 9.5 days (one at 6 days), with an average 40% of cost reduction; 60% to 70% less than the cost of a new drillwell.