Acid Fracturing Analysis Model And The Interpretation Method Of Stopping The Pump Pressure

As one of the most efficient stimulating techniques for carbonatite reservoirs, acid fracturing has been highly paid attention to and widely applied to reservoirs all over the world. However, the development of fracture diagnoses and evaluation techniques after acid fracturing according to pressure decline analysis is extremely slow. The pressure decline analysis for acid fracturing well is such a new applied field that the existent academic models and interpreting techniques can not fully satisfy the need of pressure decline analysis for acid fracturing well.Based on the analysis of existent G-function analysis method for fracturing well, this paper come up with a set of new analysis theory and interpreting techniques for acid fracturing well. The techniques can overcome the shortcomings of G-function analysis method. For example, the leakoff calculating method of fracturing fluid can not apply to acid fluid, the influence of temperature is not taken into account within the G-function analysis method and the effect of carbon dioxide which is greatly engendered in the chemical response between acid fluid and formation rock can not effectively be computed. However, the interpreting techniques put forward in this paper can successfully analyze the pressure decline after acid fracturing, which can greatly help the technicians with successful interpreting of the acid fracture parameters and correct evaluation of the acid fracturing results as well as optimizing the reservoir stimulation.This paper not only do a systemic study about the pressure decline analysis after acid fracturing for acid fracturing well but also adopt a set of new research approach on this study. The pressure decline analysis method after acid fracturing for acid fracturing well is a kind of "curve fitting" method, which has combined direct problems and anti-direct problems. First, by supposing the unknown parameters, such as acid fracture length, fracture width, this paper sets up the leakoff model for acid fluid before and after shut-in, derived the mathematic model for acid fluid flow and the chemical response between acid fluid and formation rock, establishes the fracture and formation temperature models before and after shut-in. Based on these mathematic models, this paper successfully calculates the pressure decline curves after acid fracturing in accordance to material balance equation of acid fluid in acid fracture and pressure decline model after acid fracturing; Second, by making use of the actual pressure decline curves after acid fracturing, this paper fit the fracture and reservoir parameters by inversing, coMParing and iterating on the basis of approximation of function theory. The data that has been obtained when the error function get the minimum has reflected the actual acid fracture parameters after acid fracturing, moreover, other parameters can also be interpreted on the basis of the acid fracture parameters, it is an anti-direct problem with no doubt.According to the fundamental theoretic studies, this paper has developed a set of software about the pressure decline analysis after acid fracturing for acid fracturing well. The software can successfully calculate a series of important parameters of acid fracture and reservoir, such as fracture length, fracture width, fracture height, closing pressure, leakoff coefficient, fluid efficiency and so on. Through the examples given by this paper, it has verified the validity and reliability of the interpreting methods and techniques as well as the software given in this paper, which has great theoretic and practical significance to the development and application of pressure decline analysis after acid fracturing for acid fracturing well.