Exploratory Well Perforating Negative Pressure Design Methods Research

Underbalance perforation now becomes an industrial criterion. The underbalance difference makes formation fluid produce an underbalance blasting backflow in the moment of perforation. The backflow washes out the residue of detonation and cleans the formation nearby the hole, so that it opens the conduit of oil. It also avoid the fluid and the solid phase in the well to enter the formation and the block effect resulted by fluid or solid, so it protects the reservoir and improve the flow potential effectively. As to the prospecting well, under balance completion appears to be much more important. Whether the underbalance completion of a prospecting well succeeds or not directly connects with formulating exploration plan of a reservoir, even a discovery of a new reservoir. The key point of optimization design of underbalance perforation is to establish the underbalance difference, and it often includes the minimum underbalance difference design and the maximum underbalance difference design. The minimum underbalance difference is established on whether the hole is clean or not, and it also connects with the reservoir pressure, the reservoir temperature, the reservoir permeability, the perforating parameter, the rock mechanics parameter, the fluid property parameter, and the perforation size and so on. In the wildcat area, because the geologic parameter of the prospecting well and the neighboring well's data are unclear, the design of underbalance perforation in a prospecting well is much more difficulty than that in a field development well. So, we must establish the geologic parameter especially the reservoir pressure and the rock mechanics parameter so as to make the design of underbalance perforation in a prospecting area.In this text, we make an explorative research in obtaining the rock mechanics parameter from core test in laboratory, and we propose the test procedure and the methods to advance the test accuracy degree. After comparing different methods of obtaining the rock mechanics parameter, we conclude that we can use well log information to establish the rock mechanics parameter in prospecting areas and we develop the method of using acousticwave log information to establish the rock mechanics parameter and the transformation law between dynamical rock mechanics parameter and quiescent rock mechanics parameter. By analyzing contributing and affecting factors of abnormal pressure in reservoir, we obtain the method of using man-made earthquake data to calculate the reservoir pressure and how to advance the calculation accuracy degree. Considering the distinguishing feature of prospecting wells, we develop the method using magnetotelluric exploration data to calculate the reservoir pressure. Actually, it's very difficulty to calculate the reservoir pressure accurately. In an actual project, we have to combine several methods to gain a comparative accurate result. By using finite element technique, we explore the instant non-steady high-speed backflow behavior in underbalance perforation and develop the minimum underbalance difference design method which bases on the critical Reynolds Number skin cleaning principle. At the same time, we establish a coherent model of the maximum perforation underbalance pressure based on the rock plasto elasticity and the hole non-Darcy flow dynamics. Following the hole's mechanical stability law, we also propose the method to design the maximum underbalance pressure based on the critical equivalent plastic straining. Based on the above-explored theories in connection with underbalance perforation design in this text, we compile a program to calculate the underbalance difference and use it in well L150 of XinChang gas field. The technical application shows that the proposed methods to design the maximum and the minimum underbalance pressure in this text are substantially advanced contrasting with former empirical methods. The program of underbalance perforation design can meet engineering demands and has great applicative values.