Title : Permeability reduction threats and the opportunity to enhance well productivity in geothermal tight sandstone reservoir
Abstract:
Introduction: Reservoir Permeability is a lifeline of hydrocarbon in a reservoir in which fluid travels through to wellbore. hence, any changes in nearby wellbore formation permeability will be tangible through oil rate at surface. If this effective permeability changed negatively, a reduction in oil rate will occur and will not be desired by any company. A drastic reduction in well productivity has been noticed in 6J-Area (tight sandstone reservoir). This reduction in permeability is due to mechanical and chemical formation damage mechanisms. In literature, those mechanisms are documented but still not well understood. Reservoir Hydraulic fracture stimulation practice has proved to be a success to create highly conductive channels in the formations having very low permeability values as well as improving well hydrocarbon recovery across the united State and Europe for decades. This technology became an essential application in North Africa particularly (Sirte Basin) after the discovery of deep tight sandstone reservoirs. The aim of this study is to assess a tight sandstone reservoir formation before and after hydraulic fracture treatment and the magnitude of the productivity enhancement and recovery increment.
Method and/or Theory: Well XX-9 has been chosen for work over due to sever well bore damages and, hence dramatically production losses. Also, all necessary data is available such as laboratory work on core. In Dec-2008, well XX-9 was stimulated with alcoholic acid and showed a significant improvement to 2,155 BOPD with 400 psi WHP on 1" choke but the initial production of about 4,000 BOPD was not restored, and, therefore, it was decided to go ahead with hydraulic fracturing (HF) stimulation. An effective hydraulic fracturing design is a key to achieve the expected results in low permeability reservoirs. All relevant available static and dynamic data were gathered to optimize the fracking input parameters and two and three dimensional models were developed in the three candidate oil wells (XX-9) in north Gialo field (Sirt Basin) operated by Waha Oil Company.
Results, Observations, Conclusions: In conclusion, the hydraulic fracture can be considered as a very successful stimulation job practically and economically for low permeability sandstone reservoirs with an increase of well flow rate of double increase. Alcohol acid stimulation has restored back some production which is 53.87% from initial production. Therefore, this method was not as effective as desired to apply on entire field. The well has shown about 9-fold improvement in the productivity index from 0.7 STB/D/psi before frac to about 6.1 STB/D/psi after frac. The corresponding absolute open flow potentials are 2,879 and 25,928 STB/D, respectively.
Novel/Additive Information: Based on data analysis, the oil production rate of the three selected oil wells is improved dramatically by four to ten times with a significant decrease in the formation damage near the wellbore. The success of the frac. treatment is largely due to efficient candidate selection, project management, and systematic application of existing hydraulic fracturing techniques.
