The Study on the Well Dormancy Happened in the Majiagou Limestone Reservoir in Sulige Oilfield

In most cases, the wells with high production often behave as a rapid pressure recovery and a shorter time for flow back process because their more sufficient and persistent energy for driving the fracturing fluid flow back from the welldown. However, a “Well dormancy” behavior happened in several wells with high production in the limestone reservoir in Sulige oilfield. The “Well dormancy” performed that the fracturing acid fluid injected into the reservoir could not flow back from the wellbore at the first period, lasts 1 to 3 days, after the treatment, then the fracturing acid fluid flowed back suddenly and the wellhead pressure increased rapidly. On the contrary, that case did not happen in the gas well with low production. In order to understand this “Well dormancy” phenomenon, this paper analysed some factors influencing fluid’s flowback performance. Through the comparison with the normal ones, it was found that the permeability of the reservoir is the key factor leading to this phenomenon. Based on the leakoff experiments, it was found that the filter cake developed on the fracture walls is the direct cause lead to this “well dormancy” phenomenon. In addition, experiments for testing the break times of filter cakes were carried out. The experimental results showed that the filtercake’s break time was nearly equivalent to the well dormancy time. In order to avoid this case happen again, there are two optimistic advices, increase pump rate of acid fracturing and improve the performance of the breaker, be proposed.