Hydro Fracturing

Bottomhole pressure measurement and analysis Various modes of fracture propagation can be inferred from straight-line periods that develop on log-log plots of net pressure versus time. These modes characterize different fracture shapes. Fracture closure and fluid leakoff parameters can be determined from the analysis of fracturing pressures resulting from closure (pump-in/flowback [PI/FB]) tests. Chapter 9 provides additional fracturing analysis information. Collection and analysis of fracturing pressures are facilitated by the monitoring vehicles provided by service companies. These vehicles are equipped with computer hardware and software that can digitize, display, analyze and record relevant data. The successful application of any method of fracturing pressure analysis relies on the accuracy of the fracturing pressure data. For a quantitative analysis of the data, a sensitivity level on the order of 5 psi and an accuracy level on the order of 25 psi are generallysufficient. In particular, the bottomhole fracturing pressure and magnitude of the least principal stress (fracture closure pressure) must be known before the net pressure can be calculated. An error in either of these can result in an incorrect net pressure and incorrect fracturing pressure analysis. The sampling rate affects the amount of data that must be acquired. The fastest time is required for collecting microfracturing pressures because the pump times are typically short and closure can occur quickly. Single injection periods can be as short as 3 min; however, multiple PI/FB tests may be required. In the microfracturing case, a sampling period of 2s is desirable; 15 to 30 s may be acceptable. The execution and evaluation phases of a fracturing treatment tend to last for a significant period of time, and the sampling period can be longer than a microfracturing sampling period. Fracturing treatments typically last 0.5 to 12 hr. One