English abstract
Amin formation in Harweel area is composed of two packages of conglomerate (upper Amin conglomerate and lower Amin conglomerate) with a sand horizon in between (intra Amin sandstone). This division is based on the variation of petrophyisical data like density logs, neutron logs and sonic logs. Amin thickness is highly variable across Harweel area for which five wells have been used for the correlation using rate of penetration (ROP) logs. The main objective of the study is to map Amin conglomerate across Harweel area based on the seismic interpretation and thereby to analyze the drilling issues faced while drilling through Amin conglomerate and to recommend a way forward to minimize them in the course of future drilling.
Seismic horizon interpretation has been carried out for Natih E, upper, lower Amin conglomerate, intra Amin sandstone and top salt. Time maps have been created for these horizons wherein some faults were picked using different attributes like ant-tracking to highlight the faults.
From the operational side, drilling through Amin conglomerate is very difficult and challenging due to various reasons. Conglomerate is very thick and hard and therefore, drilling through the hard conglomerate such as Amin conglomerate creates high torque. Up to 4-5 bit are used to drill the conglomerates. Deviation through the hard and thick formation is difficult and also expensive due to the time and cost besides damage that might be caused to the tools. For instance, in well A-20 H1, 16 bits were used to drill the conglomerates that were very expensive. Drilling in conglomerates is slow as evidenced by the average ROP is about 2-4 m/h. Moreover, Amin conglomerate is deep and hence time consuming to run in hole (RIH) and pull out of hole (POOH) while drilling through 121/4" hole from top Amin to the salt.
Many bits have been tried to enhance the performance of the bits and to select the appropriate one. MM75DH or MM75DMH bit delivers the best performance in terms of depth drilled and ROP. It achieves the best performance if it is combined with geoforce motor which is a special design with high torque for better performance and characterized with low speed to avoid damage to bits.
Alternatively, air drilling technology has been tried in the field 'A' to see whether there is an improvement in its performance. It uses air to drill non-reservoir formation with an intention of reducing drilling cost by increasing the rate of penetration. However, air drilling has not been further pursued because of many limitations such as the presence of floaters.
In short, drilling issues of Amin conglomerates can be minimized by selecting the performance of the best bit and avoiding directional drilling through such hard and thick conglomerates. However, deviation can be allowed in Dahaban or in the salt which is soft. In addition, the wells to be drilled should be planned where Amin conglomerate is thin.
