The Research Of Fracturing Theory And Application Technology Of Yulin Gas Field Ancient Ages

Yulin gas-field, a large gas field found in Ordos basin, one of Changqing's four main gas fields, is one chief gas resource zone of the West-East Gas Pipeline Project. For the reservoirs with low permeability and formation pressure as Ordos, hydraulic fracturing is an essential approach for improving well production. So improving the effective stimulation technology for low permeability gas resource is researchers' key subject, and also the Strategic demand of petroleum industrial's development.Research and improvement of the fracturing techniques and technology for Yulin low pressure gas reservoir can not only provide powerful technology brace and approach, but also can play an important role in improving single well's output of Palaeoid low pressure gas reservoir and reservoir's composite economic benefit. Further more, it can also provide technology reserve for low permeability reservoir's exploitation, a research route and reference for formation stimulation in Ordos basin reservoir.This article starts with the actual geologic characteristic of Palaeoid reservoir, considering the demand of fracturing technology in Yulin, and especially does an in-depth and systemic study on the contents below: the technology of fracturing quantitative selection of well and layer, the model of multi-laminar fracturing, the technology and theory of controlling fracture height, backflow mechanism about proppant, evaluating the pressure drop and so on. The achievements are as follows:(1) Through the statistics, evaluation and analysis on the geologic characteristic of Palaeoid reservoir in Yulin, the early fracturing data and the production test data, with the methods of gray correlative and fuzzy mathematics, we set up a model of quantitative selecting well and layer on enhancing fracturing effect about Palaeoid reservoir in Yulin with artificial intelligence approach, and formed a suit of methods of selecting fracture well and layer, considering reservoir characteristic and treating parameters.(2) Based on Kirchoff's first law and second law, we established a model of distributing flow in the multi-layer hydraulic fracture process, which successfully achieved the aim of flow's dynamic distributing for the initial and redistribution. Considering multi-layer fractures extending at the same time, we set up a mathematic model of multi-vertical splits which can extend dimensionally, and compiled a relevant calculation procedure.(3) With the knowledge of linear elastic fracture mechanics and mathematical equations and on the assumption of P3D, we set up a model of fracture height with the introduction of dramatic stress intensity formula, and investigate the factors which can affect the extension of fracture height in this zone.(4) We established a mechanical model of proppant backflow in the process of fracture fluid flowback, and set up a calculating model of wellhead pressure in the course of compulsive flowback, which provide the criterion for checking parameters of fracture flowback and selecting optimal choke. We also built a mechanical model of gas-well's sand flow during the production.(5) With the research and analysis on traditional model of pressure decline, we improved the traditional method of G function analysis; Considering the fracture fluid's compressibility and discharging immediately after fracture, we established PKN and KGD models through two-dimensional analysis, and developed a new analyzing and interpreting technology.(6) Based on the consideration of non-Darcy flow and long-term conductivity, we built a mathematical production forecast model of fractured gas-well, put forward the fundamental principle of matching fracture parameters by the gas-well's production, and fitly got prop-fracture's parameters through the production data obtained after fracturing.