Reservoir Parameters Inversion Based on Fracturing Operation Parameters
Authors: Hu Jing-Hong , Zhao Yong , Wang Lei , Li Da 
Published: March 2015

Abstract
Reservoir parameters can be accurately obtained by well test. However, well test is a cumbersome process with a long time period and induces some influences on the oil field production. Though small-scale fracturing test can also acquire reservoirs and fracturing fracture parameters, it is not be realistic to carry out small-scale fracturing test for each well. If the fracturing operation information (fracturing operation curve) can be directly utilized for calculating reservoir parameters, the complicated study on the well test and post-fracturing pressure analysis may be avoided. In this paper, based on the fracturing operation curve and operation parameters, a new inversion model was established by employing the theories of fluid mechanics, rock mechanics and gas reservoir engineering and material balance principle. The model can be used for calculating the dynamic changes of reservoir or fracture parameters with operation time. In this paper, the fracturing operation data of two wells were used. The calculated results show that reservoir permeability around fracturing fracture decreases with the increase in operation time and the slope of curve will level off to a constant value in later. By using the results, it can not only optimize the subsequent fracturing design, but also provide the important reservoir information for the researchers of well test. It is significant to evaluate the subsequent production and allocate reasonable production capacity. Furthermore, it can avoid unnecessary yield loss.

Introduction
Hydraulic fracturing technology as one of the most effective measures is used to increase production and enhance oil recovery in a low-permeability reservoir. The method is applied more and more widely. Highly viscous liquid is poured into a well through the high-pressure pump unit on the ground and injection rate greatly exceeds the formation of absorptive capacity. Therefore, a high pressure is formed at the bottom of the well. When the pressure surpasses geostress near the bottom hole and tensile strength of rock, artificial cracks is formed in the formation. If sand-carrying agent is continuously injected into the well, the cracks propagation will continue and propping agent is continuously filled into hydraulic fracture at the same time. Thereby, sand packed fractures with high conductivity are formed in the formation.
If not fracturing, single well production is very low and doesn't reach industrial production standards in a low permeability reservoir. If the reservoirs of low taste need to be effective developed, it is necessary to carry out economization development. Of course, the effective development methods are necessary. Geometry of artificial fracture and relevant parameters of the reservoir can be effectively obtained through well testing, but well testing operations for each well is obviously not economical and realistic[1, 2].
The related parameters of the reservoir and crack can also be acquired by small fracturing test, which will bring excessive economic loss as well as well testing operations. The parameters of the artificial fracture and reservoir can be calculated based on pressure drop curves after fracturing, but it needs shut-in and the other operations and not possible to obtain pressure drop curves after fracturing for each well[3,4].
How to carry out reservoir parameters inversion based on fracturing operation parameters and predict productivity of single well has important theoretical and practical significance for judging fracturing effects and planning productivity development. In this paper, firstly, the relationship between bottom-hole pressure and construction time is calculated based on the relationship between wellhead pressure and construction time. Then, reservoir parameters are obtained by the principle of material balance.