Investigation And Application Of Multistage Hydrajet-fracturing In Oil And Gas Well Stimulation In China

Multistage hydrajet-fracturing combines abrasive jet perforating and hydraulic fracturing to perform separate, sequential fracture stimulations without mechanical packers. It can reasonably place fractures according to geological condition, and then accurately treat them. Without packer, it uses dynamic isolation to seal flow into target, saving operating time and lowering operating risk. Therefore, the process not only adapts to stimulate open hole, but effectively treats liner or cased completions. The mechanisms and fluid dynamics of multistage hydrajet-fracturing technology are investigated with numerical simulation and laboratory experiments. More than 30 oil and gas wells have been successfully treated using this technology since 2007. On average, three hydraulic fractures with total 120m proppants were placed at strategically selected locations in well, typically several hundred meters apart without sealing equipments. The deepest treatment in oil well 203-19 in Zhongyuan oilfield, using tubing string, was 3692m, and surface pressure reached 88MPa. Significant stimulation results were achieved in these wells. For example, production increased by more than 50 times after stimulation to the gas well XS311H in Sichuan oilfield. The oil well 92-2 in the Zhongyuan oilfield, which had been a dead horizontal well, has been revived using this technology with average oil production of 15 tons per day. Multistage hydrajet-fracturing stimulation shows promising feature for horizontal, vertical, deviated, and even multilateral wells. Introduction Recently, more and more attention has been paid to the development of low permeability reservoirs in China. Stimulation treatment has been the main method exploiting these reservoirs. In some oilfields, almost every well needs fracturing or acid treating. In recent years, multistage fracturing in horizontal wells and vertical wells becomes a preferred stimulation method to increase oil production (Li Gensheng et al. 2009). Common methods of stage fracturing include temporary plugging fracturing, limited entry fracturing, mechanical packer assemblies, and so on. Temporary plugging fracturing is appropriate for open-hole stimulation. However, this method is difficult to control the location of crack initiation along wellbore. Limited entry fracturing is suitable for many new wells completion, especially wells with thin beds. It is necessary to optimize the perforating scheme and calculate cave friction accurately. Mechanical packer assemblies are mainly applied in cemented-cased wells, and seldom used in bare-hole or slotted liner wellbores. In addition, some packers are likly to be sticked during stripping operation, increasing potential risk. Hydrajet-fracturing technique (HJF), as an alternative stimulation method, does not require mechanicial packers and can achieve several stages fracturing treatment in only one service trip. Now HJF has proven to be an economical, effective, and low risk multistage fracturing process. The HJF method was put forward in 1998 by Jim B. Surjaatmajda et al., Hallibuton engineers (J. B. Surjaatmadja 1998). They did many laboratory experiments and oilfield tests in Texas and New Mexico of United Stated successfully (Jim B. Surjaatmadja, et al. 2002). In the past decade, HJF application has expanded around the world. There are many successful cases in complex structural wells, either hydraulic fracturing or acid fracturing treatment. A number of cases applied coiled tubing delivering the BHA safely and quickly (Mc Daniel, B.W. et al, 2004). Remarkably, in 2003 its first offshore