WL reservoir located in the north of China is an important exploration area of PetroChina. The reservoir depth is about 1300–1500m. The average formation thickness is 20.4m. The porosity is 7.9–12.9% and the average is 11.9%. The permeability is 1.71–4.40mDc. The reservoir belongs to low porosity and low permeability reservoir. The physical property and the results of previous oil testing indicate that the WL reservoir can only be developed through fracturing.
In use of the numerical simulation software of systematic fracturing and based on the offtake pattern and well spacing in WL reservoir, the development index is predicted for systematic fracturing when separately considering various conditions such as favorable fracture or unfavorable fracture, water-injection well fracturing or non-fracturing. Choosing the recovery percent in 10 years as the main evaluation index, and combined with the initial recovery percent and oil recovery rate, the fracture parameters of systematic fracturing in WL reservoir were determined. The reservoir systematic fracturing schemes have been applied in four oil wells in 2006, and the stimulation effects in 3 wells are obvious. The fracture parameters simulated through production data after fracturing is consistent with the design parameters, which indicates that the design parameters are reasonable and it has significance for effective development in WL reservoir.
By present hydraulic fracturing technology has advanced to reservoir systematic fracturing from single well's stimulation treatment. Reservoir systematic fracturing has become an important economical treatment for low-permeability reservoirs since a great deal of wells have uneconomical productivity without fracturing. Therefore, it is very important to consider the requirements of fracturing treatments when programming the exploitation project for one new oil field or the future adjustable project for the old field.
Reservoir numerical simulation with hydraulic fractures is the basis of the optimum design of systematic fracturing. The numerical simulation software of systematic fracturing is developed, in which nine-spot pattern, five-spot pattern and rectangular well pattern are considered and both favorable and unfavorable azimuth of hydraulic fractures are included.
The fracture parameters of systematic fracturing in WL reservoir were determined. The main objective of this research is to study and apply the fracture parameters of systematic fracturing in WL reservoir.
Well pattern of oil reservoir is five-spot pattern, the basic input data is in table 1. We consider two types of fracture extension directions which are along connection line of production wells and connection line of production well and water injection wells. The former is favorable fracture and the latter is unfavorable fracture. They are shown in Fig 1. This paper defines fracture penetration rate to characterize the effects of fracture length to fracturing effects. In favorable fractures, penetration rate is the ratio of fracture length to production well spacing. In unfavorable fractures, penetration rate is the ratio of fracture length to the distance of production well and water injection well.
