1st Research Conference - Gulf Coast Section SEPM

Fluid System Compositions: Drilling, completion, and enhanced recovery
fluids react with natural (authigenic) cements in rock pores and these reactions
can affect the quality and production of any reservoir. This effect is particularly
true in the Woodbine in East Texas where a wide variety of natural cements are
present (Fig. 2). In some locations, Woodbine sandstones are sensitive to fresh
or sodium-based drilling and completion fluids because of the presence of the
swelling clays illite-smectite or smectite. In other areas these clays are absent
and no swelling problems exist. Certain areas are characterized by sensitivity
to either HCl or HF acids (whether used in mud clean-up or stimulation) due to
the presence of specific sulfides or oxides in the pore systems. The sensitivities
of Woodbine sandstones to waters and acids are not uniform across East Texas
but vary from area to area and from zone to zone. Thus drilling and completion
fluids should be designed on a local regional scale.
Drlll Stem testing Results: Diagensis can have a significant effect on drill
stem testing results. The presence of authigenic cements often causes poor drill
stem test results. There are instances when DST results should be ignored and
well completion encouraged. Poor DST's in the Woodbine result from any or all
of the following: (1) secondary porosity, (2) silica overgrowths [Fig. 2A], and (3)