This paper describes the optimization of a well placement in a 4 m thin complex sand reservoir, using a point-the-bit rotary steerable system, real-time LWD imaging, and 3D geosteering software in well Chermingat A02 drilled by Newfield Peninsula Malaysia Inc. Real-time, at-bit gamma images 1 m from the bit proved crucial in providing early structural interpretation for geosteering decisions. Higher resolution density images further refined the structural interpretation. A geosteering consultancy service, based in the customer's office, provided the subsurface team with guidance throughout the geosteering process, which led to the successful delivery of the well objectives.
The advanced, intuitive 3D geosteering software was used to create a geological model based on offset data and geological surfaces. This local geological model was updated continuously throughout the drilling process, based on the best match between modeled and actual logging-while-drilling (LWD) sensor responses, to reveal local bed dip, bed thickness, and faults. Changes in the well trajectory were seamlessly communicated to the directional drillers on-the-fly by means of a two-way down linking system to the point-the-bit rotary steerable system, while on-bottom drilling ahead continued with no drilling interruptions. This new level of efficiency, using at-bit images immediately integrated into an intuitive geological modeling package with full support from the geosteering advisors, resulted in rapid geosteering decisions with no downtime waiting for a decision from town. The team achieved 500m (1,640 ft) MD of high quality reservoir, thus meeting the objective of the original well plan.
This strategy and operational efficiency resulted in a cost savings of ﹩812,000 (USD). The methodology, lessons learned, and experience gained from this well were applied successfully in the next drilling campaign in East Belumut A02 and in subsequent wells on the East Belumut platform.
Introduction
The Chermingat field is located in the Malay basin offshore Trengganu, Malaysia (Fig. 1). Newfield Peninsula Malaysia Inc. planned three wells in 2007 to produce oil from the Chermingat field. One of these wells, the Chermingat A02, was planned as a horizontal well to penetrate the J18 reservoir and the maximize drainage of this production zone.
Traditional geometric wellbore placement in extended horizontal wells within the target pay sand can be particularly challenging because the ellipse of uncertainty at the toe of the horizontal section can be as much as 5 to 7 m. This challenge is exacerbated in thinner pay zones, especially when the uncertainty in the geological earth model is high. The true vertical depth (TVD) uncertainty at the total depth (TD) of this well is 3.19 m.
Various methods and tool applications were reviewed to determine the best and most efficient way to deliver these wells online for oil production. The Chermingat A02 well plan, after numerous iterations, was deemed particularly challenging in terms of drilling and geological understanding.
The Geo-Pilot® XL point-the-bit rotary steerable system and an at-bit gamma-ray imaging tool, (ABG™) system, in combination with the intuitive Stratasteer®3D geosteering service, were deemed fit-for-purpose to assist in delivering optimum wellbore placement in the 4 m thin J18 reservoir.
Case Study: Chermingat A02
The target production sand, J18, is a 4 m thin sand in the Chermingat field. The J18 sand is a distal tidal flat depositional environment; the sand thins to somewhat shaly in part toward the toe of the horizontal.
