Abstract
Shale oil and gas reservoirs are developed by MFHWs. After large-scale hydraulic fracturing, it is hard to forecast the production rate using the theoretical method. In the engineering application field, the empirical method of DCA is often used to forecast the production rate of shale oil and gas produced by MFHWs. However, there are some problems in using DCA, like how to find out the proper decline model and switch point of two contiguous flowing periods and how to deal with the unsteady operation condition which causes a lot of uncertainty in production forecast. In order to solve these problems, firstly, a straight line model, representing the linear flow period in the life cycle of shale oil and gas produced by MFHWs, in the Q , lg q coordinate system is proven to be theoretically proper. Secondly, the duration of the linear flow period is verified to be over 10~15 years by using an analytical model to do the calculation with the method of Monte Carlo random sampling taking a large amount of parameter combinations of Eagle Ford shale oil and gas reservoirs into calculation. And a field data analysis of Barnett and Eagle Ford also shows that the duration of linear flow period can be more than 10~15 years. Thus, a method of production forecast taking advantage of the straight line feature in the Q , lg q coordinate system is raised. After practical use, it is found that the method is robust and can increase the forecast efficiency and decrease the manual error. Moreover, it can increase the accuracy of production forecast and deal with some unsteady operation conditions. Therefore, this new method has good promotional value in the engineering field.
Highlights
Shale oil and gas reservoirs are developed by MFHWs
We suggest that no matter what unsteady operating condition is encountered, keep the production forecast using the last seen straight line feature in the ðQ, lg qÞ coordinate system, because the changed operation condition cannot change the flowing period
With the purpose of increasing the production forecast accuracy of shale oil and gas reservoirs developed by MFHWs, this paper completed the theory of DCA and raised a more efficient DCA method to provide a reference for the engineering field
Summary
Shale oil and gas reservoirs are developed by MFHWs (short for multifractured horizontal wells). A straight line forecast method with a theoretical basis which can be broadly used in shale oil and gas reservoirs produced by MFHWs is newly raised By using this method, the efficiency and accuracy of production forecast can be increased and at the same time the applicability of unsteady operation condition can be increased. The research result of MFHW production performance in shale oil and gas reservoirs shows that there are mainly three flowing periods: early-stage transient flow period, linear flow period, and boundary-dominated flow period [1,2,3,4]. An analytical model is used to calculate the time duration of the linear flow period In this process, the reservoir parameters and fluid PVT parameters are gained from Eagle Ford shale oil and gas reservoirs, and the Monte Carlo random sampling method is used to determine a large amount of parameter combinations. Equation (6) shows a linear order relation of cumulative production Q and logarithm of production rate q
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