Currently, a major part of our oil and natural gas production comes from wells in tight naturally fractured or fissured formations. In many cases, the commercial viability of these wells depends on the success of hydraulic fracturing. Properly designed fracture treatment enhances the production from these wells substantially. However, the complexities of fracture treatment of such reservoirs often lead to premature screenouts due to accelerated leakoff in the fissures from stress sensitivity. Normally, the fissures dilate with increased treatment pressure and the permeability of these fissures increases exponentially as suggested by Walsh1 model for stress sensitive fissures. Such stress or pressure sensitivity of fissures need to be diagnosed and remedied before a successful optimum treatment can be achieved in these formations.
Conventional minifrac analysis of injection pressure and decline pressure often helps in diagnosis of such pressure dependent leakoff case. The original Nolte decline analysis was for wall building fluids or for a constant leakoff case. When this analysis is applied to the pressure dependent leakoff case, the fluid efficiency is over-predicted suggesting inadequate pad volume and pump rate requirements. Such designs with inadequate pad volumes often cause proppant dehydration and premature screenout.
This paper presents a modification to Nolte's decline curve analysis that helps in the diagnosis and evaluation of pressure dependent leakoff. It is also observed that such analysis leads to substantially lower fluid efficiency calculation resulting in increased pad volume and treatment rate. By applying the suggested method of analysis an empirical relation between the net pressure and fluid leakoff coefficient can be obtained.