Research On High Acid Pressure Of Controlled Seams In Tahe Oilfield

Tahe Oilfield is a carbonate reservoir with large, deep buried depth, poor physical properties, strong heterogeneity, and the reservoir is mainly used for acid fracturing stimulation. Since the minimum level of principal stress contrast between pay formation and barrier bed is small with the high thickness of oil and gas reservoirs, the longitudinal crack height is very large during acid fracturing, and the crack length is relatively short. This will not only lead to orthogonally crossing the reservoir, but also the crack is often less than the crack length of ideal, resulting in acid fracturing efficiency is not satisfactory. Therefore, we adopt the artificial barrier control technology of acid fracturing to improve the success rate of acid fracturing, holding the fracture height, building long fractures, which is certain significance to guide field.This article belongs to the content of national science and technology major project "In-Situ Stress Distribution and Crack Height Control Technology Research" (2011ZX05014-006-004). For Ordovician carbonate reservoirs in Tahe Oilfield, the theoretical study of acid fracturing design with controlling crack height is conducted. The main work and achievements are as follows:(1) Based on the thermal equilibrium principle, the temperature field models of wellbore and crack affected by the heat from acid-rock reaction are respectively established. And the affects of the injection fluid parameters and the working fluid flow parameters on temperature distribution at bottom of a well and in fracture are calculated and analyzed by numerical simulation, which provides real-time parameters for simulating three-dimensional extension of the fracture created by acid fracturing, the migration of diverting agent, and acid-rock reaction rate in carbonate rock reservoir.(2) The settlement rules of diverting agent in carrying liquid are studied, and the pump-off time that the formation of the artificial barrier needs and the geometry parameters of the artificial barrier are simulated.(3) According to the mass conservation theory, fluid mechanics, elasticity theory and the fracture mechanics, a three-dimensional extension model of the acid fracturing crack with the artificial barrier is established, which can simulate the three-dimensional extension process and obtain crack extension data.(4) Based on the acid-rock reaction dynamics and the mass conservation of H+, the convection-diffusion equation which simulates the flow of acid in fracture and acid-rock reaction is set up to study the concentration distribution of acid and obtain the effective acid distance.(5) By integrating comprehensively the above mathematical models and taking temperature field, velocity field, diverter migration and artificial interlayer formation, reaction dynamics and acid concentration distribution into consideration, the simulation calculation procedures of acid fracturing crack extension by a multistage alternate pump injection of acid are worked out in the VB6.0 software platform, through which the acid fracturing crack propagation with artificial barrier in Tahe Oilfield can be simulation. It is the focus of this paper.(6) Compared with other technologies which are used to control fracture height, it is proved that artificial barrier has a good effect by calculating and analyzing the effects of related factors on crack propagation.