Identifying the Root Cause of a Deepwater GoM Infant Sand Control Failure
Authors: Stair Craig , Morphy Paul , Chipperfield Simon , Harris Stephan , ONeal Dean , Pewitt Michael 
Published: December 2007

When sand control failures are associated with high-cost deepwater completions, the need to understand the mode of failure is of paramount importance. This paper illustrates how Shell attained this understanding by adapting the Root Cause Failure Analysis (RCFA) approach, commonly used in Shell's downstream chemical business, to the sand control failure of a Gulf of Mexico sub sea well. The basic steps of a RCFA are Data Collection, Problem Identification, Problem Description and Causal Analysis. Using the RCFA process in the upstream petroleum industry has rarely been conducted in the past.

In the process of identifying the root cause failure, the detail required for the RCFA explores the underpinning assumptions for commonly accepted processes and techniques. In the case of this failed well, the detailed analysis of the RCFA led to additional learnings that will not only reduce the incidence of failures in the future but also improve completion design generally. This paper provides a summary of these findings.

In conclusion, based on this RCFA, guidelines are provided to identify when this technique should be applied, how this approach could be improved in the future and the necessary factors (staff, data, and management sponsorship) required for this process to be of maximum value to the corporation.

Introduction

During the initial unloading of Well A through the subsea flowline, large quantities of sand and proppant were produced, which cut out some production equipment on the host TLP. The sand and proppant were of sufficient particle size and quantity to confirm a sand control failure. Because the failure was unexplained, and the cost of remediation was estimated at $30,000,000, a formal RCFA effort was then chartered to investigate the sand control failure.

This paper initially presents a description of the well events (Well Background). This is a detailed section since later in the paper it will be necessary to point to multiple events that led to the failure. Secondly, this paper describes the four major stages of the RCFA process (RFCA Process Overview). On the basis of the RCFA work, the likely cause is then stated (Likely Failure Mode), and evidence supporting this failure mode presented (Evidence for the Likely Failure Mode). Finally, the impact this project will have on subsequent wells is discussed from both a technical and work process / cultural perspective.

Well Background

The following well history is based on the compilation of numerous records taken during the drilling and completion operations. These records include morning reports, surface pressure and downhole pressure data, pumping records (including stimulation), job logs, tally books and interviews with personnel. For reference a completion diagram is provided in Figure 1 and a log section in Figure 2.

Well Design

Well A was a development well with an exploratory deepening. The main target sand (A sand) was already proven; the deeper sand (B sand) was untested. If zone B was successful, the plan was a smart well with both the A and B zones completed in the 8 5/8" liner. If zone B was unsuccessful, the fallback completion was a single A sand Frac and Pack completion.

Drilling

The well was S-shaped with a 57 degree hole angle through the targeted completion interval in the A sand. A 90 degree azimuth change was made to line up all the subsurface targets.

The 57 degree well angle and the 22 degree bed dip created an angle of almost 80 degrees between the A Sand and the wellbore. The 224 measured ft of net pay section was 48 ft of True Statagraphic Thickness (TST).

Running the Liner

Two-hundred and sixteen joints of 8–5/8" 60.7# P110 / 13Cr110 casing were run and became differentially stuck across the A Sand at 24,641' MD (float equipment began at 24,491' MD), with the liner top at 15,381' MD. The casing shoe stuck between the 4th and 5th lobe of the 6 A sand lobes.