Reservoir Characterization of Camar Sand, Henderson Field, Concho County, Texas: A Stratigraphic Trap in a Lobate Delta System

Hughbert Collier, Arthur Cleaves, James McIntire

The Camar sand in Henderson field, Concho County, Texas, produces from a stratigraphic trap formed by the updip pinch-out of a crevasse splay-subdelta lobe complex. The sand is part of a river-dominated, high constructive lobate delta system.

The reservoir-quality Camar sand is a medium to fine-grained, well-sorted, quartz-cemented sublitharenite. Quartz is the dominant framework grain. Shale clasts (10-25%) and chert grains (2-7%) are common. Porosity is equally divided between intergranular and moldic (dissolved shale clasts, chert, feldspar, etc). Pores are generally clean.

Much of the reservoir has interbedded shaly, very fine-grained, non-porous, impermeable laminations. Vertical permeability is one to two orders of magnitude less than horizontal permeability.

The Camar sand produces from both a distributary-channel and a channel-mouth-bar facies. The two facies plot distinctly on porosity-permeability graphs.

The two facies have several significant differences. The distributary-channel facies is the better reservoir rock (193 md and 18.5% porosity vs. 54 md and 15% in the channel-mouth bar). Permeability variations are greater in the channel-mouth bar facies. Samples with 14% to 16% porosity have permeabilities that range from 3 to 90 md. Ankerite cement is common only in the channel-mouth bar facies.

Reservoir characterization of such fields is usually based solely on wireline logs, since cores are seldom available. However, integration of the core and log data allowed several refinements to be made to the reservoir model. Net feet of pay was reduced, and vertical permeability barriers were discovered in the reservoir-quality sand.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.