ABSTRACT

The Willamette Industries 33 #1-Alt. well located in Rocky Mount Field, Bossier Parish, Louisiana, was a recent successful Smackover Gray Sand test. Image logs, rotary sidewall cores, and a conventional electric log suite were collected over the Gray Sand interval for analysis. As its name suggests, the Gray Sand is dark gray in color, poorly to moderately well sorted, lower very fine- to lower fine-grained laminated sandstone. Thin section analysis of cores indicate that physical compaction has altered depositional texture and reduced pore volume. Core porosity ranges from 4.0% to 9.4% with an average porosity of 6.7%. Quartz is the most abundant framework grain followed by argillaceous rock fragments (Fig. 1). Framework grains with minor abundance include plagioclase feldspar, volcanic and plutonic rock fragments, and locally chert. Grains identified in trace amounts include ooids, mica, potassium feldspar, and heavy minerals. Core samples are quartz-rich sublitharenites (Folk, 1980).

Quartz overgrowths are generally the most common cement in all of the core samples (Fig. 1). The overgrowths are generally large and significantly reduce pore volume. The second most common pore-occluding material is bitumen (Fig. 2). It is found in minor to common amounts in all the samples except from 11408 feet. Bitumen is seen as an irregular, slightly botryoidal grain coating in the core SEM photomicrographs (Fig. 2). Less common cements include ferroan dolomite, siderite, pyrite, titanium oxides, anhydrite, barite, ferroan calcite, and authigenic clay minerals. XRD has identified 5 to 8 weight percent clay minerals with illite composing approximately 2/3 of the clay and the remainder being chlorite. Klinkenberg permeability ranges from 0.010 to 0.125 millidarcies.

The interpreted depositional environment of the Gray Sand interval in the Willamette well is lagoonal to nearshore marine to shoreface transition. Image logs reveal ball and pillow structures, bioturbated sands, shallow marine bar deposits, as well as cross-bedding reversals indicating tidal influence. Natural and drilling induced fractures are also indicated on the image logs. Fractures are predominately found on the ENE and WSW borehole walls and align with regional faulting. Structural dip at the Willamette well is 2° at 184° azimuth.