Improved Reliability of Drilling Operations Using Managed Pressure Drilling Technology: A Case Study in a Brownfield Environment
Authors: Malloy Kenneth P. , Roes Vincent 
Published: October 2008

The original Mars A-14 well was drilled and completed in 1996. The well was worked over in 2000 because of a sand control failure. In 2003, the well was again shut in due to increased sand production and decreased oil production. In 2004, after slot recovery operations, the M1/M2 objectives were re-drilled.

Development drilling after years of production has become increasingly challenging because of depletion and difficult wellbore geometry. It is unavoidable to intersect both depleted and virgin pressured sands in the same interval. High mud weights required for wellbore stability coupled with a narrow Pore Pressure / Frac Gradient window elevate the risk of lost circulation, stuck pipe, and well control problems, making any sidetrack an expensive and potentially hazardous endeavor. Three sidetracks in close proximity to one another in the Gulf of Mexico in 3,000 feet of water were drilled into the same production horizons on the Mars Tension Leg Platform. Forty six drilling days were spent attempting to drill Sidetrack 1 (ST01), with 61% of that time attributed to unplanned, nonproductive activities that included wellbore instability, lost circulation, and kicks. Over 6,000 barrels of synthetic based mud were lost to formation.

Nearly 32 days were spent attempting Sidetrack 2 (ST02), with 60% of the time attributable to unplanned non-productive time; primarily fighting lost circulation and wellbore instability. Over 3,000 barrels of synthetic based mud were lost.

Both Sidetracks 1 and 2 were drilled in the conventional manner. Managed Pressure Drilling (MPD) technology was employed to drill Sidetrack 3 (ST03) over a 33 day period. Seepage accounted for losses of 600 barrels of synthetic based mud. There were no recorded incidents of lost circulation, kicks, or wellbore instability that would have otherwise interrupted drilling operations. Unplanned non-productive time was less than 2%.

Significant improvement in drilling efficiencies were realized utilizing Managed Pressure Drilling technologies. A direct comparison of equipment and operational technologies will be discussed.

Introduction

The Mars Tension Leg Platform is located in the Gulf of Mexico, approximately 130 miles southeast of New Orleans, in 3,000 feet of water (Figure 1). The A-14 well is an updip oil producer in the waterflooded M1/M2 (Upper Green) reservoir.

The well was originally drilled and completed in the M2 sand in 1996. The M1 sand was added during a 2000 workover for a sand control failure. Because of increased sand production and decreasing production rate, A-14 was shut in again in May 2003. In 2004, the decision was made to redrill the well to the original M1/M2 objective after recovering the slot.

The completion tubing and production tie-back were recovered, a whipstock was set, and the well was sidetracked out of the existing 11-7/8" casing. An intermediate 9-5/8" × 11-7/8" expandable liner was successfully set at 14,330' MD. Sidetrack 1 reached total depth of 21,144' (16,340' TVD), at a maximum inclination of 56 ° and departure of 10,116', when lost circulation was encountered. The lost circulation combined with hole instability problems led to loss of the bottom hole assembly (BHA).