Multi-stage Horizontal Fracturing in Casing for Low Permeability Reservoirs

Abstract

Abstract In recent years, the low permeability reserves account for over 70% of the annual new reserves of PetroChina. In 2009, the annual producing reserves and the new drilled wells of the low permeability reservoirs accounted for 70% of the total number, respectively. The low permeability and non-conventional reservoirs are characterized by high percolation resistance and poor connectivity, and may yield commercial value only after acidizing or fracturing. However, the production of acidized or fractured vertical wells is still low and the benefit is poor. The horizontal wells have the advantages of large drainage area and low pressure drop, which make the multi-stage horizontal fracturing an effective technology for the development of low permeability and non-conventional reservoirs. Most of the horizontal wells of PetroChina low permeability reservoirs are completed with casings to meet the requirement of water injection, thus the technology of horizontal fracturing in casing is crucial for improving recovery efficiency. Three principal techniques of multi-stage fracturing were developed, i.e., double-packer single-slip, packer-sliding sleeve, and hydraulic sandblast, together with four matching techniques such as multi-stage stimulation with chemical temporary-blocking gel plug, high efficiency self- diverting acidizing or acid-fracturing technique of carbonate reservoir, hydraulic fracture monitoring and evaluation, and horizontal well workover. In addition, an optimization method of fracture and well pattern was also proposed. The 3 principal techniques, 4 matching techniques, and the optimization method, effectively promoted the industrial application of horizontal wells in low permeability reservoirs.