STARR Posters
Permanent URI for this collectionhttps://hdl.handle.net/2152/125454
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Item Facies, cycle stratigraphy, and heterogeneity of the Clear Fork carbonates in Mitchell County Texas(GeoGulf conference, 2023-04-23) Fu, Q.The Clear Fork carbonate reservoirs at Iatan East Howard field are highly heterogeneous. Facies analysis and cycle stratigraphy are employed to characterize the Clear Fork Formation and reservoir heterogeneity at the field. One-dimensional (1-D), vertical stratigraphic analyses start from meter-scale cycles to cycle sets, system tracts, and then depositional sequences. A reverse process is followed to construct a 2-D framework from a 1-D stratigraphy. Ten lithofacies are differentiated. In the downdip areas, the Clear Fork Formation is dominated by subtidal facies; toward the updip, peritidal facies become more abundant and depositional facies may alternate between shallow subtidal and tidal-flat facies. Approximately 56 well-developed, meter-scale, upward-shallowing cycles were defined in the Clear Fork cores facilitated by wireline logs. Most of them have bioclast wackestone and packstone in the lower part and are capped by fenestral peloid packstone, silty to sandy dolostone, and/or dark mudrocks. Six cycle sets (high-frequency sequences) were identified, and two depositional sequences were recognized. Sequences are correlatable, but it is challenging to correlate meter-scale cycles. The Clear Fork cycles display relatively consistent thickness and facies stacking pattern plus evidence of subaerial exposure and erosion of subtidal facies, suggesting an allocyclic control and having been the result of eustatic sea-level fluctuations. Reservoir pores (porosity > 4%) commonly occur in the transgressive system tracts and lower highstand system tracts (HSTs) within individual high-frequency sequences; the upper HSTs commonly consist of amalgamated peritidal deposits and are generally tight because pores (mostly fenestral and intergranular pores) have been occluded by anhydrite and carbonate cements. These new findings contrast the previous studies showing that porosity is typically higher in the cycle-set-top or cycle-top facies (mainly tidal-flat deposits) in the formation. Reservoirs are a really discontinuous and vertically compartmented by numerous nonporous zones. Reservoir characterization is critical to improving recovery efficiency. This case study provides an insight into complex facies and cycle stacking patterns as well as stratigraphic architecture on a carbonate platform of a waning icehouse phase and can help to better understand the controls on the distribution and quality of such carbonate reservoirs.Item Application Of Instantaneous Frequency Attribute And Gamma-Ray Wireline Log In The Delineation Of Lithology In Serbin Field, Southeast Texas: A Case Study(Society of Exploration Geophysicists (SEG) Annual Meeting, 2018-09-22) Ogiesoba, O.C.; Ambrose, W.; Loucks, R.G.Although Serbin Field in southeast Texas was discovered in 1987, lithological and petrophysical properties in the southeastern part of the field have not been fully evaluated. We generated instantaneous frequency from 3D seismic data and predicted gamma-ray response volume from seismic attributes. By extracting maps of instantaneous-frequency and gamma-ray response along interpreted horizons, and crossplotting instantaneous-frequency against gamma-ray logs and integrating core data, we generated lithology maps to identify shale-prone zones that stratigraphically trapped hydrocarbons in the southeastern part of the field. We demonstrate that Serbin Field is separated into two areas: (1) a high-frequency, high-gamma-ray, and high-acoustic-impedance area in the northwest; and (2) a low-frequency, low-gamma-ray, and low-acoustic-impedance area located in the southeast. By developing a lithologic map and relating it to the corresponding instantaneous-frequency map and log data, we also show that the southeastern part of the field can be divided into three zones: (1) Zone 1, composed of ~2–8 ft (~0.7–2.7 m)-thick sandstone-rich beds of moderate frequency (25–30 Hz); (2) Zone 2, composed of high-frequency (33–60 Hz) shale-rich zones that serve as stratigraphic-trapping mechanisms; and (3) Zone 3, composed of ~5–13 ft (~1.7–4 m)-thick sandstone-rich beds of low frequency (0–18 Hz), and relatively high porosity. These methods can be applied in other areas of the field with limited well control.Item Seismic Reservoir Characterization Of The Strawn Group, Northern Part Of The Eastern Shelf, King County, North-Central Texas: Case Study(International Meeting for Applied Geoscience & Energy (IMAGE), 2023-08-23) Ogiesoba, O.C.This abstract discusses the results of combined poststack attri- butes and neural network procedures applied to the Strawn Group in the northern part of the Eastern Shelf in King County, North-Central Texas, covering an area of approximately 162 square miles (420 square kilometers). Although facies variability within the Strawn Group in King County has been described (e.g., Hattori and Flaig, 2023), the variations in elastic properties of carbonate facies have not been fully investigated. By combining a poststack model-based acoustic impedance, multiattributes and neural network procedures to predict veloci- ty ratios (Vp/Vs ratios), I show that although Strawn Group car- bonates are characterized by high impedance, they nevertheless can be separated into three main facies: (1) Platform carbonates in which Vp/Vs ratios vary from ~1.94 to 2.02, (2) Shelf-edge reef carbonates where Vp/Vs ratios are >2.02, and (3) Basinal and slope carbonates which are characterized by low Vp/Vs ratios ranging from ~ 1.88 to 1.96.Item Low-amplitude, high-frequency climatically-driven sea-level changes in the Lower Wilcox(GeoGulf conference, 2024-04-10) Olariu, I.; Smith, V.; Moscardelli, L.; Locarte, M.A.Understanding how climatically-driven changes can produce significant eustatic fluctuations, especially during periods of Earth’s history that lacked continental-scale ice sheets has been a long-time question for geologists. In this paper we use an example from Lower Wilcox greenhouse time to explain how climatically- driven short term eustasy controlled sedimentary deposition. We base our interpretations on a geochemical proxy model for orbital-scale greenhouse humid–arid climatic shifts and on palynological analysis. During the humid greenhouse phase, intense chemical weathering, more precipitation, and therefore higher sediment supply advanced the deltas closer to the shelf edge. The regressive half-cycle is characterized by the presence of Deltoidospora which indicates coastal marshy conditions. During the arid greenhouse phase, less precipitation and therefore, less sediment supply decreased deltaic progradation and favored short term marine transgressions. We see a corresponding increase in the palynological indicator Classopollis classoides, a thermophilic and thus a reliable proxy for hot climatic conditions. Low amplitudes and high frequencies excursions of sea level changes produced modest facies belt shifts recorded in 86 m of core from 2 wells in Karnes county (Moczygemba #11 and Olinick #16). Subsurface sandstone mapping based on about 800 well logs reflects short excursions of the shoreline during repeated cross shelf transits amid an overall backstepping succession.Item Controls on Mudrock Pore System Development in the Upper Mississippian Barnett Shale, Fort Worth Basin, Wise County, Texas(American Association of Petroleum Geologists (AAPG) Annual Convention, 2019-05-19) Reed, R.M.; Loucks, R.G.; Rowe, H.D.An investigation of the nanopore systems in the Barnett Shale found that the controls on pore development are in part related to lithofacies, but are also related to organic- matter properties. Sixteen Ar-ion milled samples from core in the Devon Adams No. 7 well in the Newark East Field were analyzed using scanning electron microcopy. This core begins in the upper Barnett and provides a complete section of the lower Barnett. Samples were selected based on core lithofacies descriptions and XRF chemostratigraphic analysis to ensure a complete range of lithofacies was analyzed. Quartz content averages 42% with a high of 73%. Clay-mineral content is generally low, averaging 15%. Four of the samples are relatively calcareous including two from the Forestburg limestone member. TOC averages 3.66% with a range from 0.54% to 7.42%. Siliceous lithofacies have higher TOC values than the carbonate-rich lithofacies. Calculated Ro averages 1.04% (but low-T shoulders on S2 peaks). Pore types consist of interparticle, intraparticle, and organic-matter (OM) pores. Pore type and development varies between lithofacies and to a lesser extent between spots on the same sample surface. Based on visual estimates, OM pores are commonly the dominant pore type in siliceous and argillaceous mudstones. OM pore morphology varies between kerogen and solid bitumen. Kerogen pores are generally larger, some greater than 1 µm in length, and more elongate. Bitumen pores are generally smaller and more equant. Organic matter in association with phosphatic grains appears espe- cially porous. The calcareous lithofacies, which contain less organic matter, have fewer OM pores. Intraparticle pores are present in all lithofacies, but are not common. Interparticle pores are rare and are generally less than 1 µm in size. The lack of interparticle pores in most lithofacies is interpreted to be the result of spread of ductile kerogen and occlusion by solid bitumen. Two organic-rich siliceous mudstone samples, one from the lower Barnett and one from the basal Mo-enriched mudstone, show few pores in their OM. These samples suggest that OM properties rather than simple TOC content controls pore development. Even using XRF, one nonporous siliceous mudstone sample was not di erentiated as a separate lithofacies in the initial core analysis. The conclusion that both lithofacies and organic-matter properties have an in uence on the generation of mudrock pores is important for trying to predict pore development and distribution in mudrock plays.Item Depositional Processes at the Lower Wilcox Shelf-Slope Transition Zone(GeoGulf conference, 2023-04-23) Olariu, M.I.; Zeng, H.Recognition of bypass at the shelf margin is key to deep-water exploration. This study examines the shelf margin architecture of the Lower Wilcox Group in Texas by combining 3D seismic with well log data. During the early Paleocene an extensive (40 km wide), shallow shelf platform extended across South Central Texas making it difficult for the deltas to reach the shelf edge. The seaward pinchout of the Lower Wilcox sand-rich shorefaces is about 20 km updip from the shelf edge indicating that the sand remained on the inner and middle shelf and the shelf margin grew through mud accretion. High stand conditions of sea level favored the generation of hyperpycnal flows that incised into shelf deposits, and bypassed sand onto medial and distal slopes. In areas of shale withdrawal, extensional features such as growth faults produce long, linear to arcuate strike-elongated depocenters within the hanging-walls of faults and dictate sediment delivery pathway. Our work suggests that significant volumes of deepwater sands were deposited from sustained turbidity currents initiated by direct river effluents and accumulated on the slope. High density hyperpycnal flows created multiple sand-filled slope-channel complexes 10–20 m thick and 200 m to more than 1 km wide that served as conduits for bypass to the basin floor. Unconfined, low density hyperpycnal flows deposited lobes on the slope. Lobes spread 10-20 km laterally and 2-4 km downdip, with a maximum total sand thickness of 100 m; accumulative sand thickness can be as high as 500 m. A high net-to-gross (0.5) suggests the sand-rich component of the flow was deposited on the slope, while finer grained sediment continued down the slope. The shelf-margin architecture exhibited by the Lower Wilcox sequence serves as an example of hyperpycnal flows being the primary initiator of turbidity currents for sand accumulation on the slope.