Mark D. Sonnenfeld

Parameters controlling sonic velocities in a mixed carbonate-siliciclastics Permian shelf-margin (upper San Andres formation, Last Chance Canyon, New Mexico)

We have measured the acoustic properties and mineralogic composition of 48 rock specimens from mixed carbonate-siliciclastic outcrops of the Permian upper San Andres formation in Last Chance Canyon, New Mexico. The goals were:(1)identify and model the parameters controlling the sonic velocities; (2) assess the influence of postburial diagenesis on the acoustic velocities. The variation in sonic velocity in the 0 to 25 % porosity range is primarily controlled by porosity, and secondly by the ratio of carbonate-siliciclastic material. Linear multivariate fitting resulted in a velocity-porosity-carbonate content transform that accurately predicts sonic velocity at different effective stresses. The slope of the velocity-porosity transform steepens with increasing carbonate content, which may be explained by the higher velocity of carbonate minerals. Another reason may be the property of carbonate minerals to form more perfect intercrystalline boundaries that improve the transmission properties of acoustic waves and are less sensitive to changes in effective stress. The velocity ratio VP / VS is an excellent tool to discriminate between predominantly calcitic lithologies (ratio between 1.8 and 1.95) and predominantly dolomitic and quartz-rich lithologies (ratio between 1.65 and 1.8). Gardners experimental curve overestimates, and the velocity-porosity transforms by Wyllie and Raymer underestimate, the observed sonic velocities, probably because they do not account for variations in texture, carbonate mineralogy, and pore geometry. Petrographic observations show that postburial diagenesis is minor and does not seem to significantly affect porosity. Therefore, the outcrop data set can be regarded as a proxy for the subsurface analog. These findings underline the significantly more complex acoustic behavior in mixed carbonate-siliciclastic sedimentary rocks than in pure siliciclastics where mineralogic composition explains most of the observed relationships between porosity and sonic velocity.

Seismic Models of a Shelf-margin Depositional Sequence: Upper San Andres Formation, Last Chance Canyon, New Mexico

ABSTRACT The seismic resolution of stratal geometries and facies distributions observed in San Andres Formation (Permian) outcrops in Last Chance Canyon, Guadalupe Mountains, New Mexico, is studied by seismic modeling of a published, detailed stratigraphic cross section. The outcrops in Last Chance Canyon are composed of two fourth-order depositional sequences: an aggrading carbonate bank (upper San Andres 3; uSA3) followed by a strongly progradational, offlapping mixed carbonate-siliciclastic succession (upper San Andres 4; uSA4). Each sequence comprises a number of subsidiary high-frequency sequences (fifth-order). Two alternative impedance models were used: Model A, in which all facies transitions are reflecting boundaries, and Model B, in which only time-significant surfaces act as reflectors and lateral facies transitions are represented by horizontal velocity gradients. The vertical-incidence modeling technique was used to compute perfectly migrated time and depth sections with different frequencies. Using a low-frequency wavelet (25 Hz), the sequence boundary separating the two fourth-order cycles (uSA3 and uSA4) is poorly imaged. Instead, one is tempted to incorrectly interpret an onlap pattern generated by a high-frequency cycle within uSA4 as this major sequence boundary. In addition, the 25 Hz runs show toplap and downlap lap-out patterns in an overly oblique fashion, obscuring true asymptotic stratal relationships. Both at 35 Hz and 50 Hz, profiles based on Model B image the genetic structure of both uSA3 and uSA4 relatively well. At 50 Hz, Model A incorrectly shows a transition from a ramp to a rimmed margin within uSA4. The 35 Hz models are qualitatively compared with a published Exxon Production Research Co. seismic line, located approximately 50 km along depositional str ke to the northeast. Model A shows an unexpected good match with the Exxon seismic line, whereas Model B comes much closer to the depositional anatomy observed in outcrop. Our results show that the resolution of stratal geometries and facies distributions in Last Chance Canyon is strongly related to carbonate-sandstone alternations and the way impedance contrasts at carbonate-sandstone transitions are represented.

Capillary fluid dynamics within unconventional rocks investigated by scanning electron microscopy

ABSTRACT Fresh cores from tight-rock samples of subsurface hydrocarbon reservoirs retain mobile fluids. These fluids have complex chemical compositions and a large spectrum of molecules with different diameters and polarities. When investigated using high-resolution field-emission scanning electron microscopy (SEM), the imposed vacuum over hours of time causes pore fluids trapped in the rock sample to flow and interact with the mineral matrix. This paper reports the capillary fluid dynamics effect observed on freshly milled cross sections of tight chalk at high resolution. Multiphase fluid dynamic simulations confirm the aggregation of heavier fluid molecules on the geometrical irregularities of the pore space. As a consequence of this pitfall, the differentiation of solid organic matter versus variably viscous hydrocarbons from SEM data is subject to a fundamental revision.

ABSTRACT: Multi-scale Data Integration for 3D Reservoir Modeling of Seminole San Andres Unit

The Reservoir Characterization Project on the Seminole San Andres Unit, West Texas began with the ultimate goal to integrate 12,000 feet of core, 600+ wells, a 3D seismic volume, and 40+ years of production history into an integrated reservoir management tool in 3D. This goal was accomplished through several phases: key facies from core, log cleanup, facies prediction, integration of acoustic impedance, stratigraphic-framework delineation, and iterative rock property distribution.