--> ABSTRACT: Addressing Geological and Reservoir Uncertainties in a Horizontal Well: Pre-Drill Planning and Post-Drill Production Anomalies, by Jerry G. Hardouin, Kendall C. Reynolds; #91020 (1995).

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Addressing Geological and Reservoir Uncertainties in a Horizontal Well: Pre-Drill Planning and Post-Drill Production Anomalies

Jerry G. Hardouin, Kendall C. Reynolds

The Trinity Shoal Field Cib. Carst. N Sand reservoir is a reworked distributary mouth bar in an upthrown fault trap located offshore Iberia Parish Louisiana. Estimated original oil and gas in-place in this saturated crude reservoir is 60 million barrels and 120 billion cubic feet, respectively. In 1993 Well No. 151 was drilled on the western flank of the field as a horizontal development well. During well planning, a number of uncertainties were addressed including stratigraphic variation, membering, seismic velocity gradients, structural undulations and fluid contact uncertainties.

Reservoir stratigraphy varies from clean and blocky in the central portion of the reservoir, to shaley, laminated and membered on the flanks of the field. The 3-D seismic was of limited use in target selection because of non-amplitude associated pay and seismic velocity variations in the vicinity of the proposed location. Reservoir simulation was used to predict a range of possible well outcomes using high and low case geological interpretations, corresponding to high and low case reserves.

To reduce risk, a pilot hole was drilled to select the target, then sidetracked for a horizontal completion in the better developed lower sand member. Subsequent production anomalies, pressure transient data, sidewall core analyses and horizontal well models indicate that the horizontal sidetrack did not penetrate the lower sand member, but rather penetrated the upper member twice due to the structural undulations.

Plans are to sidetrack the horizontal well and make a conventional vertical completion in both sand members in order to improve recovery.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995