Planning, Drilling, And Completing A Record Horizontal Well In The Gulf Of Mexico
Authors: Johnston R.A. , Porter D.A. , Hill P.L. , Smolen B.C. 
Published: October 2008

INTRODUCTION

Maximizing profits is the ultimate business objective in all drilling and completion operations. By far and away the biggest contributor to profits is the productivity of the well. Reliability and costs certainly impact profits; however, they pale in comparison to productivity when a rigorous calculation of net present value is performed. The simplest and most effective way to improve productivity is to increase the quantity of net reservoir exposed to the wellbore. A horizontal trajectory is the ultimate way to maximize the length of formation exposed to the wellbore.

Drilling and completion technology development over the last several years has made the use of horizontal wellbores in unconsolidated formations practical. Utilizing a unique mixture of new and existing technology, BP recently brought their first horizontal well in the Gulf of Mexico on line in record setting fashion. The planning, installation and results of this team effort are detailed in this operations oriented paper.

GEOLOGY AND RESERVOIR

The majority of the reserves in the Amberjack (Mississippi Canyon 109) field are contained in the "Green or G-sand", a very unconsolidated Pliocene reservoir. Permeability of the reservoir ranges from 300 to 1000 md with the pay zone varying from clean to laminated sand/silt/shale. The G-sand was targeted for this horizontal wellbore with a projected thickness of 40' tvd based on 3D seismic data and offset well logs.

The G-sand reservoir was deposited by a shelf-edge delta system which laid down the sediments as a series of shingled mouth bar sands separated by dipping silt beds. These depositional units are referred to as "clinoforms" (refer to Figure 1). Barriers to flow of reservoir fluids between these packages of sand and silt were predicted from 3D seismic data and well logs. The potential for reservoir compartmentalization in this type of stratigraphy was the major consideration for proposing the A-5 horizontal wellbore.

Significant differences in oil properties and water contacts in several wells drilled to date indicated that isolation of some areas was likely. While not all clinoform boundaries are sealing, the challenge for field development has been to ensure effective recovery with a minimum number of wells. The A-5 well was oriented to use a single horizontal wellbore to drain three clinoforms in the western portion of the field and planned to take the place of two or three conventional wellbores. The wellbore was oriented perpendicularly to the clinoform depositional axes with the completion interval draining all three packages (Figure 2).

A secondary benefit of the A-5 was to reduce the tendency for bottom-water production by providing additional standoff from the oil-water contact in the relatively thin oil column in the target region. Previously drilled conventional wells have typically produced water within 6 months of completion through either water coning or overrunning mechanisms.

Reservoir simulation was carried out to evaluate potential benefits of the non-conventional well and to evaluate sensitivities to reservoir description uncertainties. A cross-sectional model was used to investigate reservoir description issues including kV/kh ratio, bedding plane orientation, and clinoform boundary transmissibilities.