The Successful Application of Diesel as Horizontal Drilling Fluid
Authors: Holt Charles A. , Falmy Helmy 
Published: December 2007

This paper discusses the successful use of diesel as a horizontal well drilling fluid. Four lateral sections were drilled with diesel. All four horizontal wells are in the Sidki Field situated in the Gulf of Suez, Egypt. The lateral section consists of a low pressure sand reservoir (3.6 PPG EMW) with a static bottom hole temperature of 295 F, resulting in severe differential sticking problems in the first horizontal well while drilling with conventional Oil Base Mud (OBM). Extensive lab tests were performed in an effort to improve the filter cake of the OBM, minimizing or eliminating differential sticking problems. The pilot testing did not yield any appreciable improvements, so identifying a drilling fluid with no filter cake was pursued. Several water base drill-in fluids were evaluated, however temperature and density considerations prohibited their use. Diesel was identified and selected as the optimum drilling fluid. A combination of a low density fluid and elimination of a filter cake provided the best situation for minimizing differential sticking. Diesel was used to complete the lateral section in the first well and to drill the remaining three horizontal sections, eliminating all differential sticking problems. The results of these four wells are presented in this paper, also as well as hole cleaning issues while drilling with diesel.

Introduction

The Sidki Field is located in the southern Gulf of Suez, Egypt, (Figure 1). Sidki was discovered in January 1976, a 12 slot platform was set, and production commenced in December 1977. Eventually 9 wells were drilled from the platform, however on December 9, 1989 the platform was struck and severely damaged by a cargo ship traveling outside the shipping lane. The platform was a total loss, all nine wells were plugged and the platform removed.

Redevelopment of the Sidki Field commenced in 1993 when a new 12 slot platform was set 1150 ft from the original platform. Initially the redevelopment plans included 9 wells, all build and hold type trajectories penetrating the Nubia productive horizon. However, after drilling the first well from the Sidki B platform and confirmed with the second well, the reservoir pressure was observed to be the same as prior to abandoning the original platform. The Nubia reservoir is 1000 ft thick tilting at 30 degrees providing good gravity segregation of reservoir fluids. It was anticipated that during the 4 year shut-in period the reservoir pressure would have increased due to an active water drive. Based on the stagnate pressures observed in the first two wells, the theory of an active water drive was dismissed and a new redevelopment program was devised. The new development program included horizontal wells. Since the reservoir energy was exhausted plus the fact that gas production had plagued the original Sidki A platform production, horizontal wells were identified as a viable solution. The lateral sections would increase the exposed productive interval, while minimizing gas coning, Fig. 2.

Drilling horizontal sections in the depleted Nubia sandstone would prove to be challenging for the GUPCO Drilling Group. Redevelopment optimization had been ongoing for several years awaiting the delivery of the Sidki B platform. Mud systems and casing points had been optimized from the Sidki A drilling. These efforts were recognized when the first two Sidki B wells were drilled in 38 and 42 days respectively compared to the previous best of 72 days from the Sidki A platform. Drilling Nubia lateral sections would pose a whole new set of challenges. Differential sticking would be a major challenge while drilling the highly permeable Nubia sandstone's.

After becoming differentially stuck several times on the first Sidki horizontal well, Sidki B-4, a solution had to be identified if the horizontal program at Sidki was to be successful. Diesel was identified as the best fluid. It was the lowest density fluid readily available and clean diesel would not generate a filter cake, two of the major contributing factors to becoming differential stuck.