In Changqing gas field, it is very usual that a gas well contains many gas bearing beds, whose property is different with each other. Because of the low formation pressure and low permeability, the nature rate is so small that every well must be treated. However, when treating these multi-layer wells, the conventional separate fracturing is not effective or cost-effective, and needs long time. To make all the beds treated effectively, to improve individual well producing rate and enhance economic benefit, optimizing several kinds of separate layer treatment technology and analyzing the feasibility of commingled producing in Changqing gas field. In 2005, a new completion string has been introduced[1∼,5], which is achieved by plugging of the packers and opening of the sand blast sleeve. Using this technology and completion string, three formations can be fractured continuously, but needn't kill well. Firstly, perforating all the three gas layers at a time, at the same time assembling the completion string, then tripping it in the gas well; secondly, launching a ball to make packers set down, and fracturing the lower most layer; thirdly, launching a ball again to open the upper sand blast sleeve so that the upper layer is connected with the tubing and isolated with the sub layer, so the second layer can be fractured. Similarly, and the last layer can be treated like this step. Finally, when all the layers have been treated, unloading liquids of all layers, blowouting and producing. During fracturing, if sand plug happens, it can be solved by reverse washing. The strong point of this technology is that all the processes are made in the same string and needn't exchange string. From 2006 to 2009, the separate fracturing string with packers has been used more than 2000 vertical wells that cover 2 or 3 payer-beddings.
However, there are more and more vertical wells that contain far more than 3 layers, even to eight layers. So it is necessary to develop the separate layer string for fracturing at least 4 layers. This paper describes how to achieve this aim by intrducing new tecnnologies such as TAP fracturing technology, coiled tubing fracturing technology and modifing the initial fracturing string so that eight layers can be fractured with only one trip.