Study on the Drilling Fluid Flow Rate Allowable Range in Offshore Drilling Considering the Extended-Reach Limit

Abstract Offshore drilling has the characteristics of high risk investment, increasing the difficulties of offshore drilling design. Conventional offshore drilling fluid flow rate design method fail to consider the effects of extended-reach limit in offshore drilling. As a result, the extended-reach well (ERW) may unable to reach to the designed well trajectory length, causing potential safety hazards. Therefore, there exist a drilling fluid flow rate allowable range (DFFRAR) in offshore ERW. In this study, considering the dynamic pressure balance of bottom hole and drilling pump's rated pressure and rated power, coupled with the needs of hole cleaning, four constraint conditions of DFFRAR and corresponding DFFRAR prediction model are proposed. The predicted DFFRAR of offshore ERW must satisfy these constraint conditions simultaneously. In the end, an ERW in South China Sea is analyzed, and the well's DFFRAR is also determined. Furthermore, some optimization measures are also put forward to obtain wider DFFRAR. The results of case study show that the DFFRAR of offshore ERW in South China Sea ranges from 31.1 L/s to 35.7 L/s when the designed well trajectory length is 3243 m. In addition, the DFFRAR becomes narrower with the increase in designed well trajectory length and ROP. In contrast, the DFFRAR becomes wider with the increase in rated pressure of drilling pump and fracture pressure of drilled formation. Moreover, the window of DFFRAR will be closed if one of these constraint conditions is not satisfied. A wider DFFRAR is conductive to the offshore drilling safety. It is necessary to obtain wider DFFRAR as much as possible by taking optimization measures. This work provides a practical tool for determining the offshore ERW's DFFRAR and achieving wider DFFRAR in order to improve the drilling efficiency and obtain good economic benefits in marine environment.