Frequency amplitude spectra derived from P-wave seismic data can be used to derive a fracture indicator. This fracture indicator can be used to delineate fracture zones in subsurface layers. Mapping fractures, that have no vertical offset, is difficult on seismic sections. Fracturing changes the rock properties and therefore the attributes of the seismic data reflecting off the fractured interface, and data passing through the fractured layers. Fractures have a scattering effect on seismic energy reflected from the fractured layer. Fractures attenuate amplitudes of higher frequencies in seismic data preferentially than lower frequencies. The amplitude spectrum of the frequencies in the seismic data shifts towards lower frequencies, when a spectrum from a time window above the fractured layer and below the fractured layer is compared with each other. This shift in amplitudes of frequency spectra can be derived from seismic data and used to indicate fracturing. A method is developed to calculate a parameter t* to measure this change in the frequency spectra for small time windows (100ms) above and below the fractured layer. The Austin Chalk in South Central Texas is a fractured layer and produces hydrocarbons from fracture zones with the layer (Sweet Spots). 2D and 3D P-wave seismic data are used from Burleson and Austin Counties in Texas to derive the t* parameter. Case studies are presented for 2D data from Burleson county and 3D data from Austin County. The t* parameter mapped on the 3D data shows a predominant fracture trend parallel to strike. The fracture zones have a good correlation with the faults interpreted on the Top of Austin Chalk reflector. Production data in Burleson County (Giddings Field) is a proxy for fracturing. Values of t* mapped on the 2D data have a good correlation with the cumulative production map presented in this study.

Acid fracture conductivity and the effect of key variables in the etching process during acid fracturing can be assessed at the laboratory scale. This is accomplished by using an experimental apparatus that simulates acid injection fluxes comparable to those in actual acid fracture treatments. After acid etching, fracture conductivity is measured at different closure stresses. This research work presents a systematic study to investigate the effect of temperature, rock-acid contact time and initial condition of the fracture surfaces on acid fracture conductivity in the Austin Chalk formation. While temperature and rock-acid contact are variables normally studied in fracture conductivity tests, the effect of the initial condition of the fracture surface has not been extensively investigated. The experimental results showed that there is no significant difference in acid fracture conductivity at high closure stress using smooth or rough fracture surfaces. In addition, we analyzed the mechanisms of acid etching and resulting conductivity creation in the two types of fracture surfaces studied by using surface profiles. For smooth surfaces, the mechanism of conductivity creation seems connected to uneven etching of the rock and roughness generation. For rough surfaces, acid conductivity is related to smoothing and deepening of the initial features on the sample surface than by creating more roughness. Finally, we compared the experimental results with Nirode-Kruk correlation for acid fracture conductivity.

This study had for its aim the collection, identification, and listing of the spermatophytes growing upon the Austin Chalk formation of Collin County, Texas.