An Enhanced Gelled Acid System for Fracturing with Proppant to Increase Production in a Middle East Field

Proppant fracturing treatments in sandstone and shale formations are routinely executed. However, when carbonate formations are the target, acid fracturing is the preferred treatment method. Acid fracturing delivers a high initial production, however maintaining a sustainable production rate is a challenge in the tight cretaceous carbonate formations. These formations require highly conductive fractures to enhance production, the creation of long differently etched fractures is necessary. Certain challenges are encountered in acid fracturing including high leak-off and fast acid reaction rates. The conventional practice of acid fracturing involves complex pumping schemes of pad, acid and viscous diverter fluids to achieve fracture length and conductivity targets. A simplified and cost-effective approach to acid fracturing is designed to be deployed to wells in a gas producing formation in the Middle East. This enhanced gelled system is a single fluid system that delivers rock-breaking viscosity, slow-reactive acid, and effective leak-off control. Combining this system with proppants gets the benefits from both treatments so long as proppant embedment is taken into consideration. This enhanced gelled system reduced three fluid requirements to one by eliminating the need for an intricate pumping schedule that otherwise would include: a non-acid fracturing pad stage to breakdown the formation and generate the targeted fracture geometry; a retarded emulsified acid system to achieve deep penetrating differently etched fractures, and a self-diverting agent to minimize fluid leak-off. The enhanced gelled system was prepared with 10 and 15% hydrochloric acid (HCl) and a polymer with delayed crosslinking using a zirconium metal in unspent acid. The fluid design optimization details are included to illustrate how a single system can replace the need for multiple fluids. Rheology testing at temperatures up to 285°F, proppant settling tests for ceramic (light-weight proppant) LWP and ceramic (high-strength proppant) HSP up to 5 ppa, and static breaking were conducted. Results of the rheology and proppant settling tests with this new system exceeded expectations. Furthermore, the crosslinked system could aid acid leak-off and was delayed to reduce friction pressure so that optimal pump rates were achieved to improve fluid placement across the entire open-hole lateral stage. An enhanced gelled system is desirable to prevent acid from reacting in the near-wellbore and reaching as far out into the generated fracture as possible. Full acid reaction rate was not reached with this system until the release of the internal breaker. This study demonstrates how common acid fracturing design and operational practices can be simplified by using a cost-effective approach using a single enhanced gelled acid system.