Regional assessment of the Eagle Ford Group of South Texas, USA: Insights from lithology, pore volume, water saturation, organic richness, and productivity correlations

2016 ◽  
Vol 4 (1) ◽  
pp. SC125-SC150 ◽  
Author(s):  
Ursula Hammes ◽  
Ray Eastwood ◽  
Guin McDaid ◽  
Emilian Vankov ◽  
S. Amin Gherabati ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Volume ◽  
Water Saturation ◽  
Production Quality ◽  
South Texas ◽  
Eagle Ford Shale ◽  
Eagle Ford ◽  
The North ◽  
The Impact ◽  
Sweet Spots

A comprehensive regional investigation of the Eagle Ford Shale linking productivity to porosity-thickness (PHIH), lithology ([Formula: see text]), pore volume (PHIT), organic matter (TOC), and water-saturation ([Formula: see text]) variations has not been presented to date. Therefore, isopach maps across the Eagle Ford Shale play west of the San Marcos Arch were constructed using thickness and log-calculated attributes such as TOC, [Formula: see text], [Formula: see text], and porosity to identify sweet spots and spatial distribution of these geologic characteristics that influence productivity in shale plays. The Upper Cretaceous Eagle Ford Shale in South Texas is an organic-rich, calcareous mudrock deposited during a second-order transgression of global sea level on a carbonate-dominated shelf updip from the older Sligo and Edwards (Stuart City) reef margins. Lithology and organic-matter deposition were controlled by fluvial input from the Woodbine delta in the northeast, upwelling along the Cretaceous shelf edge, and volcanic and clastic input from distant Laramide events to the north and west. Local oxygen minimum events along the South Texas margin contributed to the preservation of this organic-rich source rock related to the Cenomanian/Turonian global organic anoxic event (OAE2). Paleogeographic and deep-seated tectonic elements controlled the variations of lithology, amount and distribution of organic matter, and facies that have a profound impact on production quality. Petrophysical modeling was conducted to calculate total organic carbon, water saturation, lithology, and porosity of the Eagle Ford Group. Thickness maps, as well as PHIH maps, show multiple sweet spots across the study area. Components of the database were used as variables in kriging, and multivariate statistical analyses evaluated the impact of these variables on productivity. For example, TOC and clay volume ([Formula: see text]) show an inverse relationship that is related to production. Mapping petrophysical parameters across a play serves as a tool to predict geologic drivers of productivity across the Eagle Ford taking the geologic heterogeneity into account.

Seismic multiattribute analysis for shale gas/oil within the Austin Chalk and Eagle Ford Shale in a submarine volcanic terrain, Maverick Basin, South Texas

2013 ◽  
Vol 1 (2) ◽  
pp. SB61-SB83 ◽  
Author(s):  
Osareni C. Ogiesoba ◽  
Ray Eastwood
Keyword(s):  
High Water ◽  
South Texas ◽  
High Resistivity ◽  
Eagle Ford Shale ◽  
Eagle Ford ◽  
Austin Chalk ◽  
Bulk Volume ◽  
Multiattribute Analysis ◽  
Quality Factor Q ◽  
Sweet Spots

We conducted seismic multiattribute analysis by combining seismic data with wireline logs to determine hydrocarbon sweet spots and predict resistivity distribution (using the deep induction log) within the Austin Chalk and Eagle Ford Shale in South Texas. Our investigations found that hydrocarbon sweet spots are characterized by high resistivity, high total organic carbon (TOC), high acoustic impedance (i.e., high brittleness), and low bulk volume water (BVW), suggesting that a combination of these log properties is required to identify sweet spots. Although the lower Austin Chalk and upper and lower Eagle Ford Shale intervals constitute hydrocarbon-sweet-spot zones, resistivity values and TOC concentrations are not evenly distributed; thus, the rock intervals are not productive everywhere. Most productive zones within the lower Austin Chalk are associated with Eagle Ford Shale vertical-subvertical en echelon faults, suggesting hydrocarbon migration from the Eagle Ford Shale. Although the quality factor (Q) was not one of the primary attributes for predicting resistivity, it nevertheless can serve as a good reconnaissance tool for predicting resistivity, brittleness, and BVW-saturated zones. In addition, local hydrocarbon accumulations within the Austin Chalk may be related to Austin TOC-rich zones or to migration from the Eagle Ford Shale through fractures. Some wells have high water production because the water-bearing middle Austin Chalk on the downthrown side of Eagle Ford Shale regional faults constitutes a large section of the horizontal well, as evidenced by the Q attribute. Furthermore, the lower Austin Chalk and upper Eagle Ford Shale together appear to constitute a continuous (unconventional) hydrocarbon play.

Investigation of Production-Induced Stress Changes for Infill-Well Stimulation in Eagle Ford Shale

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1372-1388 ◽  
Author(s):  
Xuyang Guo ◽  
Kan Wu ◽  
John Killough
Keyword(s):  
Horizontal Wells ◽  
Eagle Ford Shale ◽  
Eagle Ford ◽  
Fracture Geometry ◽  
Complex Fracture ◽  
Study Results ◽  
Stress Changes ◽  
Sensitivity Studies ◽  
Stress States ◽  
The Impact

Summary Heterogeneous stress has a great effect on fracture propagation and perforation-cluster efficiency of infill wells. Principal-stress reorientation induced by depletion of parent wells has been investigated by previous numerical studies assuming uniform biwing fracture geometry along the horizontal wells. However, recent field diagnostics indicate that fractures along the horizontal wells are generally nonuniformly developed. In this study, we investigated the impact of depletion of parent wells with complex fracture geometry on stress states, and analyzed stimulation efficiency of infill wells by using an in-house reservoir geomechanical model for Eagle Ford Shale. The model fully couples multiphase flow and rock deformation in three dimensions based on the finite-element method, incorporating complex fracture geometry and heterogeneity. We used this model to accurately characterize pressure distribution and to update stress states through history matching production data of parent wells in Eagle Ford Shale. Depletion of parent wells with nonuniform fracture geometries, which has not been researched thoroughly in the literature, is incorporated in the study. Results show that magnitude and orientation of principal stresses are greatly altered by depletion, and the alteration is uneven because of nonuniform fracture geometries. Stress reversal monitored at the center of the infill location starts after 1 year of production, and it takes another 8 months to be totally reversed for 90°. We also performed sensitivity studies to examine effects of parameters on changes of magnitude and orientation of stress at the infill location, and found that effects of bottomhole pressure (BHP), differential stress (DS), and fracture geometry of parent wells are all significant, whereas effects of the reservoir elastic property are limited. Effects of production time of parent wells are also noticeable in all sensitivity studies. This work analyzes stress-state change induced by depletion of parent wells in Eagle Ford Shale, and provides critical insights into the optimization for stimulation of infill wells.

scholarly journals Effect of freezing on the microstructure of a highly decomposed peat material close to water saturation when used prior to X-ray micro computed tomography

2021 ◽  
Author(s):  
Hassan Al Majou ◽  
Ary Bruand ◽  
Olivier Rozembaum ◽  
Emmanuel Le Trong
Keyword(s):  
Computed Tomography ◽  
Pore Volume ◽  
Specific Volume ◽  
Water Saturation ◽  
Organic Matrix ◽  
Micro Computed Tomography ◽  
X Ray ◽  
Two Samples ◽  
Before And After ◽  
The Impact

Abstract. The modelling of peatland functioning, in particular the impact of anthropogenic warming and direct human disturbance on CO2, CH4 and N2O, requires detailed knowledge of the peat structure and of both water and gas flow with respect to the groundwater table level. To this end, freezing is nowadays increasingly used to obtain small size peat samples for X-ray micro computed tomography (X-ray μ-CT) as required by the need to increase the resolution of the 3D X-ray CT images of the peat structure recorded. The aim of this study was to analyze the structure of a peat material before and after freezing using X-ray μ-CT and to look for possible alterations in the structure by investigating looking at the air-filled porosity. A highly decomposed peat material close to water saturation was selected for study and collected between 25 and 40 cm depth. Two samples 4 × 4 × 7 cm3 in volume were analyzed before and after freezing using an X-ray μ-CT Nanotom 180NF (GE Phoenix X-ray, Wunstorf, Germany) with a 180 kV nanofocus X-ray tube and a digital detector array (2304 × 1152 pixels Hamamatsu detector). Results showed that the continuity and cross section of the air-filled tubular pores several hundreds to about one thousand micrometers in diameter were altered after freezing. Many much smaller air-filled pores not detected before freezing were also recorded after freezing with 470 and 474 pores higher than one voxel in volume (60 × 60 × 60 μm3 in volume each) before freezing, and 4792 and 4371 air-filled pores higher than one voxel in volume after freezing for the two samples studied. Detailed analysis showed that this increase resulted from a difference in the whole range of pore size studied and particularly from a dramatic increase in the number of air-filled pores ranging between 1 voxel (216 103 μm3) and 50 voxels (10.8 106 μm3) in volume. Theoretical calculation of the consequences of the increase in the specific volume of water by 8.7 % when it turns from liquid to solid because of freezing led to the creation of a pore volume in the organic matrix which remains saturated by water when returning to room temperature and consequently to the desaturation of the largest pores of the organic matrix as well as the finest tubular pores which were water-filled before freezing. These new air-filled pores are those measured after freezing using X-ray μ-CT and their volume is consistent with the one calculated theoretically. They correspond to small air-filled ovoid pores several voxels in volume to several dozen voxels in volume and to discontinuous air-filled fine tubular pores which were both detected after freezing. Finally, the increase in the specific volume of water because of freezing appears also be also responsible for the alteration of the already air-filled tubular pores before freezing as shown by the 3D binary images and the pore volume distribution.

COMPARTMENTALIZATION OF THE EAGLE FORD SHALE, SOUTH TEXAS – A NOBLE GAS INVESTIGATION

2018 ◽  
Author(s):  
Guolei Han ◽  
◽  
M. Clara Castro ◽  
Toti Larson ◽  
Jean-Philippe Nicot ◽  
...  
Keyword(s):  
Noble Gas ◽  
South Texas ◽  
Eagle Ford Shale ◽  
Eagle Ford
Sign in / Sign up

Export Citation Format

Share Document