The Study of Hydraulic Fracturing Expert System in Low Permeable and Complex Reservoirs
Authors: Wang Yongli , Jiang Tingxue , Ding Yunhong , Luo Ning , Feng Xingkai , Wang Xin , Zeng Bin 
Published: December 2007

Abstract
There are a lot of low permeable and complex reservoirs in china, most of them are undeveloped up to now as a result of difficulties such as stochastic distribution of formation parameters (mainly permeability and thickness), economic risk in hydraulic fracturing decision-making, unsatisfied post-fracturing rate and relatively short effective period of production after fracturing compared with those in conventional reservoirs, etc. Consequently, an expert system of hydraulic fracturing in above mentioned reservoirs is studied in details. It mainly contains:Stochastic distribution of reservoir parameters analysis;An advanced neural network is utilized to forecast 3 dimensional fracture geometry and post-fracturing rate(oil and water) correspondingly under various conditions;Monte-Carlo method is used to perform economic risk analysis;Genetic algorithm is applied to automatically select fracturing materials and optimize fracturing treatment parameters such as propant volume, proppant concentration, pumping rate, pad percentage, etc.
What's more, above optimized parameters may also be assigned various practical limits. After that, two field cases are demonstrated in details focusing on how to use the expert system and what the results we have got. Actually, the post-fracturing rate, effective period of production after fracturing and economic benefit as well are all very satisfied compared with common fracturing technology applied in the similar reservoirs. Which verifies that the expert system of hydraulic fracturing developed in the paper is not only reliable but also feasible and if it is put in to field applications in a large scale, a lot of time may be saved and the efficiency to perform hydraulic fracturing design and treatment may be much higher than ever before, in the same time, a greater economic benefit may also be available correspondingly. So, the development level in low permeable and complex reservoirs may also be improved a lot with above mentioned expert system in the future.

Introduction
It is well known that hydraulic fracturing is an indispensable stimulating measures to develop low permeable and complex reservoirs effectively and economically. Especially in PetroChina nowadays, there are several billion of undeveloped reserves, almost every well needs to be hydraulically fractured. Furthermore, as a result of complex characteristics of above mentioned undeveloped reservoirs such as very low permeability and low porosity, very complicated pore and throat structure, severe nonhomogeneity and anisotropy, natural fracture, high clay content and strong sensitivity, very easy to be damaged during a fracturing treatment, etc., an advanced hydraulic fracturing technology must be studied. What's more, hydraulic fracturing is a very complicated and overburden task, it needs knowledge from not only in theory and laboratory but also abundant field experience, and in most cases, the later is even more important. Therefore, the study of hydraulic fracturing expert system is performed in order that the knowledge and experience of many specialists may be utilized comprehensively, and in the mean time, the work efficiency of hydraulic fracturing design and treatment may also be improved a lot.
The theory and practice of the fracturing expert system is demonstrated in detail in the paper.