The main pay of the Keshen gas field is a tight sand formation with very low porosity (2% to 7%) and permeability (0.001md-0.1md). Due to the ultra-deep formation depth and superior high reservoir pressure (greater than 116 MPa) and temperatures (above 160°C), the well construction and field development costs are very high. Therefore, stimulation treatments is essential for achieving sufficiently high production rate and the basis for justifying the costs. Natural fractures (NF) are developed in the reservoir with high heterogeneity which leads to complex production mechanism due to interaction between matrix and NFs, and causes difficulties on stimulation optimization.
To better understand the reservoir and optimize the well stimulation, the matrix properties, natural fracture, geomechanical data and stimulation data has been reviewed along with production data. Massive production history matching work has been done to evaluate the NFs. Other dynamic data like the well testing data and pressure data also reviewed to help understand NFs development in the full field scal. Production analysis was conducted to link the rock properties, NFs and wells' performance, and provided full understanding of production controlling factor in this reservoir. The post production analysis helped to understand the efficiency of stimulation. The production behavior for different stimulation strategy also have been illustrated by the simulation models to investigate the impaction on the stimualtion optimization strategy by the interaction between matrix and NFs.
The study provided a good understanding of the production mechanism in this kind of natural fractured reservoir and NF's impact on the stimulation efficiency. The heterogeneity of NF results in very different production mechanism given similar matrix petrophysical behavior. Based on production mechanism, each well requires a customized stimulation to maximize the production potential.
This study presented a case study for evaluating the production mechanism and highlighted the importance on evaluating the production mechanism on optimizing the stimulation for the naturally fractured tight reservoir.