It has often been reported that the peak production of a well drilled in tight formations is highly dependent on the fracture-contact area. However, at present, there is no efficient approach to estimate the fracture surface area for each fracture stage. In this paper, we propose a method to calculate the fracture surface area on the basis of the falloff data after each stage of the main hydraulic-fracture treatment.

The created hydraulic fracture closes freely before its surfaces hit the proppant pack, and this process can be recognized in the pressure falloff data and its diagnostic plots. The pressure-decline rate during fracture closure is mainly caused by the fluid leakoff from the fracture system into the formation matrix. For a horizontal well drilled in the same formation, with the known leakoff coefficient(s) and fracture-closure stress(es), the total-fracture surface area can be calculated for all stages to meet the requirement of the fluid-leakoff rate.

The wellbore-storage effect, friction dissipation, and tip extension dominate the early pressure falloff data. Whereas the transient pressure dominated by friction losses typically lasts approximately 1 minute, the tip extension might end after approximately 15 minutes. Therefore, falloff data should be acquired for at least 30 minutes to observe a fracture-closure trend. The fracture-closure behavior can be identified on the G-function plot as an extrapolated straight line or on the Bourdet derivative in log-log plot as a late-time unit slope. The behavior of the late unit slope depends on the pressure-decline rate, or correspondingly, to the fluid-leakoff rate. Therefore, the total-fracture surface area can be estimated using hydraulic-fracture design input values for the formation-leakoff coefficient and fracture-closure stress. The calculated fracture surface area represents the combined area of primary and secondary fractures—effectively all fracture surfaces contributing to the fluid leakoff.

We applied the approach to all stages in a horizontal well that exhibit the fracture-closure behavior. The approach shows some promise as a potential way to estimate fracture surface areas that could allow an early estimate of the expected well performance.

经常有报道说，在致密地层中钻井的峰值产量在很大程度上取决于裂缝接触面积。但是，目前尚没有有效的方法来估算每个断裂阶段的断裂表面积。在本文中，我们提出了一种基于主要水力压裂处理各个阶段之后的沉降数据来计算裂缝表面积的方法。

所产生的水力压裂在其表面碰到支撑剂填料之前就可以自由闭合，这一过程可以在压力下降数据及其诊断图中识别出来。裂缝闭合过程中的压力下降速率主要是由于流体从裂缝系统泄漏到地层基质中引起的。对于在相同地层中钻的水平井，具有已知的泄漏系数和裂缝闭合应力，可以计算所有阶段的总裂缝表面积，以满足流体泄漏率的要求。

井筒存储效应，摩擦耗散和尖端扩展支配了早期的压力下降数据。尽管以摩擦损耗为主的瞬态压力通常持续约1分钟，但尖端延伸可能会在约15分钟后结束。因此，应至少采集30分钟的衰减数据，以观察骨折闭合趋势。裂缝闭合行为可以在G函数图上识别为外推直线，或者在log-log图上的Bourdet导数上可以识别为后期单位斜率。后期单位斜率的行为取决于压力下降率，或相应地取决于流体渗漏率。因此，可以使用水力裂缝设计输入值来估算总裂缝表面积，以用于地层渗漏系数和裂缝闭合应力。

我们将该方法应用于显示裂缝闭合行为的水平井的所有阶段。该方法显示出一定的希望，可以作为估计裂缝表面积的潜在方法，从而可以对预期的油井表现进行早期估计。