Zhang Fuxiang

Prediction and Reduction of Perforating Gunshock Loads

Most wells and particularly high-pressure wells are susceptible to gunshock damage when they are perforated with inappropriate gun systems and/or under suboptimal conditions. This paper presents a simulation methodology to predict gunshock loads for tubing-conveyed and wireline-conveyed perforating jobs. When planning perforating jobs in high-pressure wells, engineers strive to minimize the risk of equipment damage due to gunshock loads. The methodology described here helps engineers to identify perforating jobs with significant risk of gunshock related damaged, such as bent tubing and unset or otherwise damaged packers. When predicted gunshock loads are larger than the admissible loads, changes to the perforating equipment or job execution parameters are sought to reduce gunshock loads. This methodology enables completion engineers to evaluate the sensitivity of gunshock loads to changes in gun type, charge type, shot density and distribution, tubing size and length, number of shock absorbers, rathole length, and placement/setting of packers, among others. Fast gauge pressure data from perforating jobs shows that when model specifications are representative of the actual perforating jobs, the predicted wellbore pressure transients are accurate both in magnitude and time. Peak sustained pressure amplitudes at the gauges are on average within 10% of simulated values. With the methodology presented in this paper, engineers can evaluate perforating job designs in a short time, and they can optimize perforating jobs by reducing gunshock loads and equipment costs. The ability to predict and reduce gunshock loads and its associated damage is very important because of the high cost associated with most wells, particularly high-pressure wells. With the software presented in this paper engineers can optimize well perforating designs by minimizing the risk of gunshock related damage and the associated rig time losses.

Study on Mechanisms of Borehole Instability in Naturally Fractured Reservoir During Production Test for Horizontal Wells

During the production test for horizontal wells, down-hole pressure will drop down significantly to induce the crude oil flowing out of the wellbore, which always leads to wellbore collapse problems, especially in naturally fractured reservoirs. Hence, some special researches on this problem were carried out. Based on the mechanisms of wellbore stability and failure criterion of weak plane, the authors established the stress state around the horizontal wellbore and mathematical model of minimum down-hole pressures required to maintain the wellbore stable. This model is complex nonlinear equations, which involves several variables, including natural fracture occurrences, wellbore orientation, in situ stress, and rock strength. The combination impacts of these variables on the minimum down-hole pressure were quantified by solving this nonlinear model. The study helps deepen the understanding of the mechanisms of wellbore stability in naturally fractured reservoir.

Quantitative Fracture Characterization Method and its Application in the Bashijiqike Formation

We describe a statistical method for determining the fracture parameters and the vertical and lateral distribution of these parameters. We examine the correlation between the fracture properties and the filtration characteristics: permeability and deliverability. The grid method is an accurate and efficient tool that makes it possible to describe the surface density of fractures in the core. The parameters determined from the core can be used to calibrate the results from interpretation of well logging data, in order to sufficiently accurately determine the nature of the change in the parameters across the entire wellbore. We have established that the permeability and deliverability of the deposits clearly depends on the fracture spacing and the fracture surface density within the Dabei block of the Kuqa depression.