This reference is for an abstract only. A full paper was not submitted for this conference.
Stimulation of tight gas sandstone reservoirs is a challenge due to many variables contributed into acidizing efficiency such acids type, concentration, volume, stages, injection rate, reservoir temperature, fluids, and heterogeneity, clay type and content, and soaking time. The presence of authigenic clays in reservoirs necessitates proper design of acid treatment to avoid undesirable interaction of these clays with acids and released to cause pore plugging. Therefore, stimulation fluids need to be properly selected to avoid potential adverse results in these tight reservoirs.
The objectives of this study were to: investigate effectiveness of various acid recipes to stimulate Devonian sandstone tight gas reservoirs, determine the optimum acid formulation, and recommend the best practices to enhance stimulation treatments in gas wells.
Extensive laboratory experiments (compatibility, stability, solubility, corrosivity, and coreflooding) were conducted on sandstone cores recovered from gas reservoirs to assess the effectiveness of various acid formulations (organic, inorganic, and mud acids) and additives in enhancing gas relative permeability. A new acid treatment was developed and created wormholes in tight cores and resulted in increasing cores permeability by more than 12 fold. This recipe promoted reaction with silicate more than with clays to avoid potential of by-products precipitation while maintaining cores integrity. However, full strength mud acid found to cause core disintegration and sanding. An organic clay stabilizing agent was effective in stabilizing clays and preventing precipitation of acid reaction by-products. Experimental results are very promising and promoted field trials.
This study proposed an effective stimulation formulation for enhancing production of gas wells with low permeability or suffered from formation damage. It gives some guidelines on better practices for stimulation design to reduce flowback time needed to lift spent acid and help to achieve maximum production. Several candidate gas wells were selected for field trials using the proposed stimulation treatment. This paper will discuss results of the field trials, upon execution, along with damage diagnosis for the wells which were showed unexpected low productivity.