Research And Application Of Loss And Channeling Prevention Cementing Technology In Dagang Oilfield

With the continuous development of oil and gas exploration technology, more and more complex strata, with different pressure profile, emerge in exploration and development. Blowout and lost circulation always occoure at the same time. Because of waterfooding in the old oilfield, wellbore pressure profile is very complex in some new drilling oil and gas wells. As a result, narrow safety density window, lost circulation and gas channeling always occur simultaneously during the cementing process, which not only affects the quality of cementing, but also reduces the productivity of oil and gas wells, serious and even lead to the scrapping of oil and gas wells, resulting in huge economic losses. Thus, it is very important to solve the problem of the coexistence of leak and channeling. This paper preferred anti-channeling leak-proof cement slurry system and improve the cementing process to solve the problem of leak and channeling in cementing process.Dagang Oilfield has more than50years of development history. The main producing formation is the sandstone oil group of the Shahe street and Banqiao Formation of the tertiary in the development zone, upper Minghua town in a part of blocks. Use acid fracturing stimulation and waterflood development. The information provided by the drilling programme showed that the cementing operation conditions of the multi-pressure system has the following main characteristics:fault block production buried layer depth difference; geothermal gradient difference, high bottomhole static temperature; abnormal formation pressure caused by water injection, the lack of basic design data; trajectory changes, more casing levels, complex process, narrow safety window; depth changes, long cementing interval, more targets, high quality requirements; difficult to achieve the partition stopping injection measures.By anti-channeling system and process research, we get the following conclusions:1. If there is no exact formation pressure, we can use the drilling fluid density and the equivalent density of the pressurization capacity to estimate fracture pressure, which is a viable option to achieve balanced cementing operation; 2. In the case of the lack of exact bottom hole circulating temperature, through the outlet temperature of drilling fluid before finishing drilling, the outlet temperature during drifting, the outlet temperature after running casing, revise comprehensively slurry design temperature (preferably with temperature tester);3. Adjust the drilling fluid performances before cementing, control circulation flow rate less than the drilling fluid annulus velocity corresponding to the flow rate, multi-cycle circulation does not affect wellbore stability, which can effectively improve the degree of purification of the wellbore and cementing displacement efficiency;4. Low annular velocity combined with the rheology cascade matching displacement technology, that is suitable for cementing requirements on narrow safety pressure window, and to ensure the displacement efficiency, higher annular velocity can be obtained good displacement effect when the drilling fluid rheology is satisfied to cementing requirements;5. Low-density cement slurry system has good engineering performances, can be combination using in accordance with formation pressure characteristics, satisfy development wells cementing requirements and balance pressure cementing design requirements;6. Testing results show that the latex cement slurry system of active oil and gas wells have a good role in channeling; weighting spacer can effectively increase oil and gas layer stable, as to reduce gas channeling; using high quality drilling fluid is easy to displacement, conducive to improve the quality of cementing; composite displacement technology can reduce annular pressure to prevent the leak in cementing process, and help to improve the displacement efficiency.