An experimental study to reduce the breakdown pressure of the unconventional carbonate rock by cyclic injection of thermochemical fluids

Commercial production from unconventional reservoirs needs massive fracturing operations. Therefore, long horizontal wells are drilled, and multi-stage fractures are created to achieve the desirable production rates from these reservoirs. One common and major problem in most of the unconventional reservoirs is the high breakdown pressure due to the reservoir tightness. When fracturing these types of rocks, the hydraulic fracturing operation becomes much more challenging and difficult. In some scenarios reaches to the maximum pumping capacity without generating any fractures. In this study, a new approach to reduce the breakdown pressure of tight rocks is introduced and compared with the conventional method of fracturing. The new method incorporates the injection of thermochemical fluid in a series of cycles to create micro- and macro-fractures. The cyclic experiments performed in this study were concluded with the recording of breakdown pressure in each case. The post-treatment analysis using medical Computerized Tomography (CT) showed that multiple fractures were created due to the pressure pulse created in the thermochemical reaction. Results showed that the breakdown pressure of the rock decreases with the increasing number of cycles. The proposed method of cyclic thermochemical fracturing reduced the breakdown pressure by 33% in one-cycle, 41% in two-cycles, 53.5% in three-cycles, and 69% in four-cycles, when compared with conventional method of fracturing. An empirical relationship is also presented between the number of cycles of thermochemical fluid injection and the breakdown pressure of the rock.