Successful Implementation of a Novel Low-Viscosity Retarded Acid System in a Depleted Reservoir – Case History from Mexico

Abstract

Abstract This paper describes the planning and execution of a challenging well stimulation operation on a well in the southeast Mexico basin. The job was successfully executed despite complex conditions and the involvement of multiple services, including Coiled Tubing (CT), downhole tools, and fluid services used in efforts to solve a limited wellbore–reservoir communication. The stimulation design included first-time operator implementation of a chemically retarded acid system proving that depth of penetration can be maximized in an open hole long interval carbonate reservoir using a Hydrochloric Acid (HCl) blend with low viscosity and a nonpolymeric water soluble modifying agent. 1 ½ in CT with a milling tool was used initially in an attempt to overcome mechanical resistance while re-entering the well completion. Subsequent trials to spot and inject fluids with the CT resulted in some success from the first acidizing treatments. The main challenge included designing and implementing a customized matrix acidizing intervention to limit the Near-Wellbore (NWB) spending and opening a pathway in a slotted liner completion with a severe mechanical obstruction. Placement of the reactive stimulation fluids required the application of proper techniques to reduce initial pumping pressure and establishing communication into a carbonate formation. Despite bottom-hole conditions restricting reservoir injection, a comprehensive analysis and operational preparation played a major role in successfully executing this acidizing intervention. Stimulation resulted in a five-fold production increase with a stable post-stimulation wellhead pressure indicating improved wellbore-reservoir communication. Results demonstrated significant advantages to acid stimulation jobs that include chemically retarded HCl without gelling agents or emulsifiers. These improvements include: (a) reduced risks associated with formation damage or HSE concerns if applying only gelled or diesel emulsified acids blends; (b) deployability in high treating pressure wells where pipe friction losses are a major consideration; and (c) achieving maximum acid retardation and deep penetration. This achievement highlights the potential of conducting successful stimulation jobs where an acidizing solution may not normally be the first option in wells with challenging downhole environments restricted to flow.