High-Dogleg Rotary-Steerable Systems: A Step Change in Drilling Process

Abstract

Abstract Directional drilling has long evolved from the days of Drilling primarily with rotary assemblies, motors and turbines to regular use of rotary steerable systems (RSS). Spears estimate that RSS decreases drilling time by 50% on average (no sliding intervals) and overall well time by 25% (good quality borehole enabling smooth casing and wireline runs).However current rotary steerable systems available in the market have several limitations: Maximum Dogleg severity capability for RSS drilling 8.5in or 8.75in hole sizes from major service companies is about 6.5 to 8° /100ft in normal formations. In case of soft formations or excessive borehole enlargement these figures drop significantly and BHA is tripped out of hole for running PDM. Most RSS require a cement plug to be in place to perform consistent and reliable sidetracks. This results in additional time and trips for the operator. Controlled kick off from vertical is not possible with RSS that require a gravity vector defined to seek TF. This results in quick course corrections and higher T&D. Steering through highly inter-bedded formations close to horizontal is challenging to conventional RSS due to limited DLS resulting in POOH. This paper discusses the new generation of fully rotating RSS that has twice the dogleg severity capability of any current RSS systems (up to 15°/100ft). This new technology enables deeper Kick off lowers the horizontal displacement significantly (by 50% or more compare to current RSS), decreases overall measured depth and improves ROP. In addition to this, this new technology has proven its directional versatility by performing open hole sidetracks, saving cost and operating times. It has repeatedly demonstrated its ability to kick off accurately from vertical, land the well precisely on target depth and execute closed loop trajectory controls while drilling lateral sections. A number of case studies are covered in this paper with results from the field trials of this unique technology. With these capabilities every driller's dream to drill more complex well profiles in single run without the need to trip out of hole with time and cost savings will become reality. Present Day Technologies and Limitations At present any well planned with high dog legs (>10°/100ft) is drilled with positive displacement motors for a good reason - PDMs have the capability to deliver consistent and reliable doglegs. Typically these wells are delivered with a minimum of three BHAs. The vertical part of the well bore is drilled with a conventional rotary assembly or vertical seeking RSS or a positive displacement motor set to very low bent or straight housing. Upon reaching the kick off point depth, BHA is pulled out of hole and a PDM with high bent housing of 1.83 ° or 2.12 ° is run and the curve is drilled with slide rotate intervals to landing point. Once the landing point is reached the BHA is again pulled out of hole and a Motor with low bent housing or a conventional RSS is used to drill and geosteer in the lateral. Figure 1 shows pictorial representation of this process.