--> Identifying Compartmentalized Sections of Lower Vicksburg Reservoirs and the Potential for Directional Drilling in McAllen Ranch Field, Hidalgo County, Texas

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Identifying Compartmentalized Sections of Lower Vicksburg Reservoirs and the Potential for Directional Drilling in McAllen Ranch Field, Hidalgo County, Texas

Abstract

Identifying Compartmentalized Sections of Lower Vicksburg

Reservoirs and the Potential for Directional Drilling in McAllen Ranch Field,

Hidalgo County, Texas

Matthew McAllen, Dr. Donald Van Nieuwenhuise, University of

Houston

McAllen Ranch Field has been producing natural gas and condensate for over 50

years. Since 1960, the field has produced over one trillion cubic feet (TCF) from the

Oligocene Vicksburg formation from sandstones with 8-30% porosity, and usually less

than 1 md of permeability. Production from the field is in overall decline, yet the current

operator is undertaking new well locations and drilling programs. The Texas Bureau of

Economic Geology conducted a study of McAllen Ranch Field to model and estimate

the remaining unrecovered reserves trapped behind structural, depositional and

diagenetic low-permeability barriers. The focus of this project was to find untapped,

compartmentalized zones in the reservoirs in the north and south portions of the A.A.

McAllen lease. This was accomplished by first understanding regional and published

work done on McAllen Ranch Field and the Vicksburg formation. The next step was to

identify and correlate well logs to understand the continuity of the stacked, non-

associated gas reservoirs by understanding the typical well log response for the

different depositional facies. After the reservoirs were identified, production data was

examined to assess any potential to produce from isolated reservoir sections. Core

samples were described to understand the depositional and diagenetic low permeability

barriers, which inhibit the drainage radii of gas wells in the field. Results show that the

most potential lies within the depositional and structural trends in the southern portion of

the field that is heavily faulted and may contain isolated incised valley sandstones that

are truncated by faults. The northern portion of the field is less faulted, and has

compartmentalized sections of sand bodies that were deltaic sands that were reworked

by the northern longshore current. This sand body has diagenetic barriers, such as

tightly cemented calcite and chlorite sections. The recommendation for this field is to

partake in a directional drilling program to maximize the recovery from these tight

sandstones.