Performance of Horizontal Wells of Bentiu-3B Sandstone Reservoir of Greater Bamboo Field (Block-2, Sudan) in View of Very High Viscosity of Oil and Profile of the Horizontal Wells – Case Study

Abstract

Approximately 100 mmbbl 2P OIIP has been established in Bentiu 3B sub layer of Greater bamboo fields by various exploratotory, appraisal and Development drilling. The vertical variation in viscosity viscosity from Bentiu 1A to Bentiu 3B has been the challenge for the exploitation of established reserve by conventional wells. The exploitation strategies in Greater Bamboo Fields were conceptualized to develop the Bentiu-1 and Bentiu-3 layers separately in view of high viscosity contrast. A number of horizontal wells have been drilled to optimally exploit particularly high viscous Bentiu- 3B reservoir. Since the viscosity of the Bentiu-3B reservoir is extremely high it was decided to carry out performance study of some key wells completed as horizontal well. An attempt is made to analyse the performance of these key well completed in highly viscous oil bearing Bentiu-3B sub layer and its relation to the Horizontal well profile, proximity to the Oil Water contact, Reservoir quality in the Horizontal well, Shale layers within the Horizontal well, and the fault as well as edge water in the proximity. The paper discusses the technical details of four cases of which two wells belong to each Bamboo West and Bamboo Main fields. In the Bamboo West both the wells has been analysed in detail and it has been found that in one well the TVD was gained more resulting to the proximity to the OWC whereas the other well was planned at the edge of the structure and close to OWC and fault. In the Bamboo Main one well has been drilled in zig zag profile which has no reason based on the all available data analysed. This type of horizontal wells, although planned suitably, if not drilled perfectly result in the poor performing well. The option of sidetracking could have been better option and saved the well from disaster. The other well drilled had poor data control from the nearby well. The well trajectory was planned up dip but when drilled, initially the trajectory was up dip later become down dip. The performances of the horizontal well are greatly affected by the drain whole profile in the exploitation of high viscous oil. If the profile of the Horizontal well is maintained as gaining TVD profile i.e. down dip profile the tendency of the water to move up will be relatively lowered. This has been observed in the analysed horizontal well but their proximity to the OWC has made them more water prone. The horizontal wells drilled with Zig Zag profile, even at the best place of structure are the poor performer whereas the wells with up dip (loosing TVD Profile) may perform initially better due the structural advantage but they are susceptible for water hold up and ceased production. The paper recommends various processes and way forward to drill horizontal wells and exploit this high viscous oil of not only Bentiu-3B but also similar reservoirs.