New Approach to Drilling and Completing Horizontal Wells in Extremely Shallow and Unconsolidated Reservoirs

Abstract

This paper discusses novel approaches that resulted in the successful drilling, completion, and production from shallow and unconsolidated clastic reservoirs, offshore Brunei. As a result of these new approaches, detailed planning, continuous and open communication throughout the development project, the candidate well was drilled successfully, with the directional, well placement, and completion requirements being achieved. In addition, the application of new sand control technologies coupled with specifically engineered procedural solutions assured sand-free production at a rate above expectations. Introduction The Champion oil and gas field, offshore Brunei, is a multibillion barrel field that was discovered in 1970. Because of the thin-bedded nature of the clastic reservoirs, the field is subdivided into multiple stratigraphic units and fault blocks. Some of the least developed parts of the field are located in shallow [less then 400 m true vertical depth, subsea (TVDSS)] and unconsolidated reservoirs. Previous production from these reservoirs, from near vertical wells, resulted in poor flow rates. A development project was initiated to overcome the challenge of optimizing flow rates from these shallow reservoirs within strict and tight project timelines. This paper discusses the results from one well in the project. Horizontal openhole gravel packing (OHGP) methods have been accepted as a proven standard of completion for maximizing hydrocarbon productivity and minimizing formation drawdown in the petroleum industry for many years (Price-Smith et al. 2003; Law et al. 2005). Implementing sand-control measures in unconsolidated formations without impairing well productivity has been a challenging task from both a technical and an economical perspective (Price-Smith et al., 1998; Parlar and Albino 2000; Law et al. 2005). Gravel packing of long horizontal intervals using conventional gravel-pack tools presents a moderately complex fluid mechanics problem. The most commonly encountered problems in horizontal gravel packing are premature sandout and/or formation breakdown. These problems lead to incomplete placement of the gravel pack, with undesirable consequences ranging from higher completion costs to sand in surface facilities and long-term completion reliability problems (Vliet et al. 2001). Until recently it has not been possible, technically or economically, to drill and complete horizontal wells in certain parts of the Champion field because of the challenging nature of the formation and the proposed well profiles. To enhance production from these reservoirs, challenging well designs were required to allow landing the well by approximately 400 m TVDSS and have in excess of 500 m of drain section. Dog-leg severities (DLS) of around 6°/30 m would be required, in a field which is notorious for soft and unconsolidated formations, making directional control using conventional mud motors unpredictable. Due to the soft nature of the formations, the drilling rate of penetration (ROP) was expected to be very high. This added to the challenge of being able to land the well in the 7 m true vertical depth (TVD) best quality layer within the reservoir by using logging while drilling (LWD) technologies.