Abstract

Over the past decade, multi-stage fractured horizontal wells have been widely applied to develop tight oil and gas reservoirs. Therefore, it has become a standard practice to pump more and more numbers of treatment proppants and fluids with higher and higher pumping rate during hydraulic fracturing treatment in China, but things always did not get the expected results, field test application has displayed that not all wells production have positive correlation with increasingly treatment scales but rather lead to high costs. To investigate this problem, we established a new fracture face damage skin (FFDS) mathematical model based on the classical model of Perkins-Kern-Nordgren(PKN) and Khristianovic-Geertsma-Daneshy(KGD) using fracture mechanics and fluid coupling method. Furthormore, a new evaluation experiment by computed tomography (CT) scanning and rock mechanics and some key factors were revealed. Compared with original model the influence of FFDS on productivity was increase from 5% to 51% using new model when the permeability is 0.1mD. The results indicated the lower of permeability and the greater of impact for a specific low permeability reservoir. A case study was put forward with four different volume of proppants and fluids while different pumping ratel located in the same stratum with a same pay thickness in X tight oil reservoir. The reason was studied that some large-scale fractured well not produce that expected much oil and some small-scale fractured wells even perform better than massive treated ones owing to the fracture face damage skin. What's more, a comprehensive low FFDS treatment was put forward as following: Firstly, utilizing the low damage fracturing fluids such as slick water, low concentration and low molecular weight fluid, etc.; Secondly, optimizing the viscosity value of fracturing fluid with corresponding pumping rate for a certain permeability reservoir;Thirdly, optimizing combination between fracturing fluid and proppant types according new mathematical model; Fourthly, using such as acid-fracturing to minimize fracture face damage skin for an optimized fracture profile.

These new observations have significant implications for field development stratedies and hydraulic fracturing design. More than 45 wells have been put into field application using new technology. The performance of post-fracturing is remarkable and it has a great significance in unconventional oil and gas development in China.

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