| Hydraulic fracturing is a widely applied well stimulation technique. To obtain optimal results from hydraulic fractures, engineers must accurately predict the shape of created fractures (i.e., length, width, height).; Numerous computer simulators exist for design and evaluation of fracturing treatments. These simulators will provide reasonable estimates of fracture geometry if accurate input parameters are provided. One of the most important input parameters is fracture closure pressure, {dollar}psb{lcub}c{rcub}.{dollar} {dollar}psb{lcub}c{rcub}{dollar} is the magnitude of the normal stress acting to close a fracture. {dollar}psb{lcub}c{rcub}{dollar} varies geographically and with depth and must be determined in the field. Unfortunately, {dollar}psb{lcub}c{rcub}{dollar} cannot be measured directly but must be inferred using various techniques. One such technique is the pump-in/flowback test (PIFB).; During a PIFB test, liquid is injected into a rock stratum at a rate sufficient to create an hydraulic fracture. Following this injection, or pump-in phase, injected fluid is withdrawn from the fracture by flowing it back at a constant surface rate. During flowback and subsequent shut-in periods, the pressure data develop a distinct signature. Many hypotheses have been proposed to explain this signature and the estimation of {dollar}psb{lcub}c{rcub}{dollar} from the flowback response. However, none of these have been validated quantitatively.; In this work we develop a novel fracture model that can simulate the PIFB test. Simulated pressure responses from the model display features seen in field data. To our knowledge, this is the first time that numerical simulations of the PIFB test have been presented in the literature. Based on our simulation results we propose a plotting technique that can be used to extract {dollar}psb{lcub}c{rcub}{dollar} from the flowback pressure response. This technique yields better estimates of {dollar}psb{lcub}c{rcub}{dollar} than current procedures. |
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