Cost-Efficient Fracturing Diagnosis Using High-Frequency Wellhead Pressure Response Analysis: Case Study on Shale-Oil Recovery

Abstract Multi-staged fracturing technology in horizontal wells play a vital role in "shale revolution" of North America. High-efficient fracturing assessment is of great significance to operation and decision-making. As known to field engineers, some instruments such as permanent cemented optical-fiber system is not affordable for assessment of fracture and perforation clusters efficiency in part of unconventional projects sensitive to CAPEX and OPEX. As important down-hole tools, bridge plug and temporary-plugging materials highly affect fracture initiation and proppant placement among all stages. Dissolvable bridge plugs were widely applied in all unconventional reservoirs development in China instead of drillable plugs. The cost-effective alternative solution to on-line or post-frac validation of above tools is really required for operators. One low-cost solution was put forward in this paper. Surface high-frequency pressure gauge can be quickly connected to wellhead with maximum sampling frequency of 4000 Hz, maximum pressure value of 140 MPa and continuous sampling period of 30 days. One new data acquisition and processing methodology was proposed mainly focusing on fracture and clusters parameters. De-noising and filtering algorithm is helpful to identification of abnormal characteristics and quantitative evaluation of cluster uniformity and diverting operation. One operation pad in shale-oil basin was selected for field trial of the low-cost fracturing monitoring and characterizing solution. The well to be treated was specified as 180-cluster perforation and 38-stage pumping jobs. Pressure datasets were recorded during fracturing via high-frequency pressure gauges for filtration, processing and cepstrum transformation. With the governing model, several characteristics were further extracted and compared with available databases to further interpret all responses. Perforation clusters efficiency and diversion performance was investigated among all stages. Calculating standard deviation of pumped liquid volume among clusters of all stages was made to validate newly-developed temporary-plugging and diversion technology. The abnormal pressure drop of some bridge plugs were identified through the monitoring system during fracturing. Combining with pressure-drop transient analytics, operators further quantitatively evaluated parameters of near-wellbore fracture networks within reservoirs.