Casing Directional Drilling Using a Rotary Steerable System

Abstract

The hardware used in casing while drilling operations over the past 5 years has proved to be robust and reliable. Several directional wells have been drilled successfully with casing using positive displacement motors (PDMs), but the drilling efficiency was significantly degraded in most of them. This paper documents the drilling of the first two wells to utilize a rotary steerable system (RSS) to improve drilling efficiency when drilling with casing. Combining an RSS with casing while drilling operations seemed to be a natural way to eliminate the major weaknesses in motor bottomhole assembly (BHA) designs. Rotary steerable systems had not previously been used with casing while drilling because both are new technologies focused on different environments. Casing while drilling developed on land operations while rotary steerables have been popular for offshore projects. ConocoPhillips has drilled more than 94 wells in the Lobo trend of South Texas since 2001 using the new technique. As part of a technology demonstration project to accelerate the technology to offshore applications, two wells were drilled with an RSS. The first was an operational test conducted by drilling vertically with the RSS. The second was a full directional test with a build to 29° and then a drop to vertical, including a 100° directional turn. Introduction ConocoPhillips embarked on an active field development program in 1997 aimed at drilling hundreds of wells over the next few years in the Lobo trend of South Texas. Since that time, over 900 wells have been drilled through the Wilcox (Lobo) section ranging in depth from 7,500 to 13,000 ft. However, in 2001, after drilling about 600 wells, the drilling efficiency had stagnated. A program was undertaken to find ways to reduce drilling costs sufficiently to extend the development potential for several years. In the previous years, great strides had been made in increasing rate of penetration (ROP), drilling each hole section with a single bit, and in improving general rig operation efficiency. Any major reduction in drilling time had to address the flat time more than the "making hole" times. The most significant flat times were associated with keeping and protecting the hole, trouble time which averaged about 1.5 days per well, and casing running operations. Stuck pipe and lost circulation were the most consistent contributors to the trouble events and accounted for about 75% of the trouble time in 2000 and 2001. A casing while drilling system was chosen for a five-well pilot project to evaluate the impact that this technology might have on the particular problems encountered at Lobo. Sufficient progress was made in drilling these first wells to justify moving to a second phase of drilling. The second phase proved that casing while drilling could eliminate the formation-related trouble time experienced with conventional drilling. A major finding was the confirmation that lost circulation was almost completely eliminated, allowing the drilling of additional wells formerly considered uneconomical. The wells were not drilled trouble-free, but the trouble was associated with the mechanical equipment limitations, which were overcome on the phase-two wells. Fontenot1,2 provides more information about the Lobo field and the performance on these early wells. Full-scale implementation of the Lobo casing while drilling program was initiated by bringing in three new rigs in late 2002 and early 2003. These 15,000-ft rigs,3 built specifically for ConocoPhillips, were introduced to optimize the drilling process. They provided an increased hookload rating; much better mobility for intrafield moves, a reduced footprint, and a semi automated casing handling system. The overall drilling program at Lobo has been scaled down, with one casing while drilling rig still operating. More than 94 wells have been drilled with casing in the area. The incidents of lost circulation have been almost totally eliminated in the casing drilled wells. The difficulty of balancing lost circulation at the intermediate casing shoe while controlling a reservoir pressure of up to 15 ppg during the trip out to run production casing has been eliminated. In some cases, casing drilled wells are completed with three strings of casing when four would be required if the wells were drilled conventionally.

Designing High-Angle/Casing-Directionally-Drilled Wells

“…[1][2][3][4][5][6][7][8][9] However, there are no known cases where an offshore directional well has been drilled with the expectation that the directional BHA would be pulled with a wireline and replaced while drilling the section. [1][2][3][4][5][6][7][8][9] However, there are no known cases where an offshore directional well has been drilled with the expectation that the directional BHA would be pulled with a wireline and replaced while drilling the section.…”

Drilling High-Angle Casing Directionally Drilled Wells With Fit-for-Purpose String Sizes

“…The onshore applications range from simple vertical sections drilled with a throw-away bit on the end of the casing to fully directional wells drilled with rotary steerable systems with the capability to change the BHA without tripping the casing. [1][2][3][4][5][6][7][8][9] However, there are no known cases where an offshore directional well has been drilled with the expectation that the directional BHA would be pulled with a wireline and replaced while drilling the section.…”

“…Substantial shocks were seen in the casing directionally drilled wells in South Texas. 9 Those shocks caused damage to the rotary steerable system. Improvements to the rotary steerable systems in the last year have increased their robustness.…”

Casing Drilling Directional Wells

“…These questions arose when first considering rotary steering CwD operations: 13 • Would there be difficulties with stiffness ratios and vibrations? These questions arose when first considering rotary steering CwD operations: 13 • Would there be difficulties with stiffness ratios and vibrations?…”