No abstract

Experimental researches introduced in this paper combined the fracturing technology, which was needed in Chang-6 stratum of Changqing Oilfield, were carried out with full-size and holo-authentic. and used field jetting tools, parameters and equipments to simulate the process of hydrajet perforating and fracture initiation. All of these were different from the previous. A real-hole shape and crack structure of the near-wellbore were obtained while dissection 9 experimental samples by special tools. The experiment results shown that: The whole jetting hole is tear-drop shaped, including four parts: casing perforation, entrance sputtering section, cement necking section and main section. When fracture initiates, a slim channel with gladiate shape is extended in the end of the hole. Secondly, the sample will fracture when jetting velocity is high enough under test condition. It indicates that pressure in jetting hole increases obviously when jetting velocity increases. Thirdly, jetting flow erodes out a slim channel along crack propagate direction when fracture initiates, which increases the jetting hole length doubly and enhances the penetration efficiency. Finally, six individual channels are connected by crack when fracture initiates. It indicates that jetting channels can guide the crack initiation and extension near the well bore under the test condition. The results of the simulating experiments could be used as the design reference when jetting and fracturing in the similar stratum.

The current radial well operation technology can not adapt to high temperature, and the long tripping period and low drilling efficiency in deep well conditions.According to the characteristics of abrasive jet, a new radial drilling method is proposed in this paper, in which the abrasive jet is conveyed to the underground by CT (coiled tubing), the casing is sidetracked first, and then the formation is drilled. The working procedure is that using the CT to run the positioning and guiding tool in hole first, and then using the CT to run a steel tube in hole. When the steel tube reaches the deflector, it makes a radial turn, and the ground equipment transfers the abrasive drilling fluid to down hole through the CT. During the operation, the casing sidetracking is completed with drilling fluid with high abrasive concentration, then the abrasive concentration is reduced, and the steel tube enters the formation to complete the radial drilling. Practice has proved that when the well temperature exceeds 100°C the jet hose is easy to be damaged under high temperature and high pressure environment, resulting in leakage of drilling fluid and unable to complete the operation normally. It is necessary to select a suitable temperature-resistant jet hose. Practice has proved that when the well depth is more than 4000 meters, the pressure loss along the system increases and the jet water power from the nozzle decreases. For hard formation, the water jet is not enough for rock breaking drilling in the formation. The results show that under the same water power condition, abrasive jet has stronger ability to break rock and penetrate hard stratum than water jet because it contains solid particles with higher hardness and density. At the same time, the abrasive water jet with suitable abrasive concentration and water power can be used for casing sidetracking. The casing sidetracking and formation drilling are combined to simplify the process. Experiments show that the types of abrasives, abrasive concentration, drilling fluid composition, drilling fluid water power, injection time affect the casing window opening and formation drilling effect. The method introduced in this paper solves the technical problem of water jet radial drilling, which is easy to break jet hose at high temperature (180°C) and can not break rocks due to the decrease of water power in deep wells (4500 m), and expands the application scope of radial drilling technology. Secondly, it simplifies the working procedure and opens up a new construction technology.