Abstract

The Cotton Valley sandstones have been targeted for hydrocarbons since the 1940s. The reservoir was initially considered poor due to its low permeability and was uneconomical to drill. Since then, further technological advances in hydraulic fracturing allowed the Cotton Valley sandstones to become a prolific, profitable play, renewing further drilling and exploration across the northwestern and northern Louisiana region.

In this research, mineralogical and clay restrictions on porosity and permeability in Lower Taylor sandstones of the Cotton Valley were studied from a core (Worley Estate 29H–1 well), Blackburn Field, northwestern Claiborne Parish. Twelve billets were cut at intervals throughout the Taylor Sandstone starting at 10,150 ft and continuing to the top off the Taylor Sandstone at 10,035 ft. The samples taken from specific intervals having associated porosity and permeability data that will be evaluated throughout this research. Each of these billets underwent X–ray fluorescence (XRF) and X–ray diffraction (XRD) analyses with those intervals containing greater than 3% total clay weight additionally analyzed using scanning electron microscopy (SEM) imaging. All methods were used in conjunction to determine cement mineralogy and trace element geochemistry to aid in determining porosity and permeability destruction in the formation’s matrix. Thin sections were created at each interval to analyze mineralogical digenesis and its association with reservoir properties as well as gain a better understanding of the depositional environment. Well log evaluation and techniques were also used in this study to create a calibration between physical core description and the log response. This relationship allowed specific recognition of lithology changes in the core and the reflected log response.

By understanding mineralogy and the diagenetic stages of the rock, the study will determine mineralogical restrictions of porosity and permeability and its relation to hydrocarbon accumulation within the Lower Taylor sandstones of the Cotton Valley Group in Claiborne Parish, Louisiana.