Sorrento Field Research Articles

The Integration of Capillary Pressures and Pickett Plots for Determination of Flow Units and Reservoir Containers

Summary This paper shows how to construct lines of constant capillary pressure, process speed, pore-throat aperture, and height above the free water table on a Pickett plot. The integration of these properties allows the determination of flow units and reservoir containers and illustrates the important link between geology, petro-physics, and reservoir engineering. The concept of flow (or hydraulic) units and reservoir containers has been used in the oil industry with a good deal of success during the past few years. The process or delivery speed k/ϕ can be used in many instances to define a flow unit. Correlation of flow units between wells helps to establish reservoir containers and forecast reservoir performance. We show that a Pickett crossplot of effective porosity vs. true resistivity should result in parallel straight lines for intervals with constant process speed k/ϕ. The slope of the straight lines is related to the porosity exponent m, the water-saturation exponent n, and constants in the absolute permeability equation. From the straight lines, it is possible to determine capillary pressures and pore-throat apertures directly for each flow unit at any water saturation. Pore throats at 65% water saturation compare very well with Winland r35 values. The method has not been published previously in the literature. Building lines of constant k/ϕ allows the display of complete capillary pressure curves on the Pickett plot, including regions that are and are not at irreducible water saturation. Previous empirical methods for determining the absolute permeability of a given interval assume that the water saturation is at irreducible conditions. This paper presents a technique that allows us to estimate absolute permeability even if the interval contains moveable water. The use of this technique is illustrated with previously published data from the Morrow sandstone in the Sorrento field of southeastern Colorado and carbonates from the Mission Canyon formation in the Little Knife field of North Dakota. We conclude that flow units can be determined reliably from the integration within one single log-log graph of Pickett plots, capillary pressures, pore-throat apertures, and Winland r35 values.

Morrow sandstone reservoir characterization: A 3-D multicomponent seismic success

A 3-D, 3-C seismic survey over a clastic valley‐fill reservoir in the Pennsylvanian Morrow Formation at Sorrento Field, Colorado, could mark a major turning point in the use of seismic technology for reservoir characterization in this area.

Abstract: Characterizing a Morrow Sandstone Reservoir Through Stratigraphic Interpretation of 3-D Seismic Data, Sorrento Field, Colorado 

Sorrento field, southeastern Colorado, contains an estimated 21 million bbls of original oil in place in the Pennsylvanian Morrow sandstone. The reservoir consists of a coinplex of stacked channel sequences within an incised valley. Interpretation of 3-D compressional seismic data has outlined the configuration of the incised valley and provided essential information about the characteristics of the rocks that fill it. This seismic interpretation provides stratigraphic details on the compartmentalization of the four flow units which explain the multiple fluid contacts and variable performance of wells in this field. reservoir is encased in marine mudstone; normal compressional seismic data are not capable of imaging reservoir rock because the acoustic impedance is not sufficient to distinguish the two lithologies. Rather, seismic modeling shows that the compressional seismic character of the Morrow interval is the result primarily of high-velocjty/hjgh-density nonreservoir rocks. The distribution of these nonreservoir rocks is critical in delineating the reservoir because the channel sandstone is bordered by reflective rocks such as floodplain deposits or high-density facies which lie outside of the valley wall. Nonreservoir rocks that are barriers to flow within the reservoir, such as carbonate-cemented zones, define the compartmentalization. The petroleum industry has been challenged to characterize Morrow reservoirs because the sandstone

Characterizing Fluvial Sandstone Reservoir Compartmentalization through Stratigraphic Interpretation of 3-D Seismic Data, Sorrento Field, Colorado: ABSTRACT

Sorrento Field, southeastern Colorado, contains an estimated 21 million barrels of original oil in place in the Pennsylvanian Morrow sandstone. The reservoir consists of a complex of stacked channel sequences within an incised valley. Interpretation of 3-D compressional seismic data has outlined the configuration of the incised valley and provided essential information about the characteristics of the rocks that fill it. This seismic interpretation provides stratigraphic details on the compartmentalization of the four flow units which explain the multiple fluid contacts and variable performance of wells in the field. The petroleum industry has been challenged to characterize Morrow reservoirs because the sandstone reservoir is encased in marine mudstone; normal compressional seismic data are not capable of imaging reservoir rock because the acoustic impedance is not sufficient to distinguish the two lithologies. Rather, seismic modeling shows that the compressional seismic character of the Morrow interval is primarily due to high velocity/high density non-reservoir rocks. The distribution of these non-reservoir rocks is critical in delineating the reservoir because the channel sandstone is bordered by reflective rocks such as floodplain deposits or high density facies which lie outside of the valley wall. Non-reservoir rocks which are barriers to flow within the reservoir, suchmore » as abandoned channel fill, define the compartmentalization. The 3-D seismic interpretation techniques that have delineated Sorrento Field and its compartmentalization are applicable to similar reservoirs worldwide.« less

Radiometric Surveying Applied to an Evaluation of Sorrento Field, Cheyenne County, Colorado: ABSTRACT

The radiometric survey was performed in July of 1994 as part of the Colorado School of Mines Reservoir Characterization Project Phase V. The 5.5 square mile field study consisted of geologic; geophysical; reservoir engineering; geochemical; 3-D seismic and radiometric investigations over the Sorrento Field. Radiometric data was acquired over the study area using a 512 cu. In. NaI detector system and four channel digital acquisition system. Twenty foot stations were acquired along the same traverses as the source and receiver lines of the 3-D seismic program. Profiles were plotted for each line. Data was normalized and Z-Transform and ratio maps were produced. A profile interpretation map indicated the presence of several lineaments possibly related to fracturing now known to exist within the study area as a result of the 3-D seismic survey. An experimental north-south profile was also obtained through the study area using a NaI detector and full spectrum analyzer capable of 60,000 CPS. Data was processed into 1000 channels of data. An analysis of the full spectrum data indicates the presence of two discrete (4 to 6 KeV) windows in the lower portion of the gamma spectrum that exhibit a consistent high response over the productive portion ofmore » the field. The normally expected low radiometric response over petroleum reservoirs appears to be a function of a general overall decrease, principally in that portion of the gamma spectrum below 1.50 MeV.« less

Reservoir Characterization Using Surface Geochemistry, Sorrento Field, Cheyenne County, Colorado: ABSTRACT

The survey was performed in July of 1994 as part of the Colorado School of Mines Reservoir Characterization Project. In addition to the geochemical survey, the study included a complete geologic and engineering evaluation, a 3-D seismic survey, an electrical resistivity survey, and a radiometric survey. Geochemical methods included soil gas hydrocarbons, pH, Eh, and soil electrical conductivity measurements. The data were analyzed and interpreted for concentration and compositional anomalies. Field analog comparisons provided additional support for the compositional characterization. With the exception of local lineaments, defining anomalies based on direct hydrocarbon concentration proved difficult due to field depletion. The indirect parameters of pH, Eh, and conductivity exhibited a greater degree of anomaly definition by identifying areas of varying reservoir potential and exposing a complex system of faults and fractures. Compositional analysis of the data yielded information regarding reservoir lithology and hydrocarbon type. Surface hydrocarbon ratios were compared to gas compositions from known Pennsylvanian and Mississippian wells within Cheyenne County. Discrimination of these reservoirs, by analog comparison, was possible within the Sorrento Field limits. The final report, released by CSM in August of 1995, asserted that the hydrocarbons and pH parameters reliably detected the major trends. The conclusion stated thatmore » the geochemical anomalies were consistent with the geologic and geophysical interpretations.« less

Reservoir Compartmentalization of the Morrow Sandstone at Sorrento Field, Southeastern Colorado: ABSTRACT

Reservoir Compartmentalization of the Morrow Sandstone at Sorrento Field, Southeastern Colorado: ABSTRACT

Tectonic and Sedimentation Model For Morrow Sandstone Deposition, Sorrento Field Area Denver Basin, Colorado

Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent major Morrow discovery with recoverable reserves estimated at over 10 million barrels of oil from an area of 3200 acres (1295 ha) at depths of 5400 to 5600 ft (1646 to 1707 m). Minor production also occurs from the Mississippian Spergen Formation, the Mississippian Saint Louis Formation, and the Pennsylvanian Marmaton Group. On the basis of subsurface mapping, productive Morrow sandstones are interpreted to be fluvial valley-fill deposits, consisting mainly at channel sandstones. These deposits are encased in marine shale and range in thickness from O to 55 ft (O to 16.7 m); net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19% and permeabilities range from 1 to 4000 md. Isopach maps of the Morrow and associated stratigraphic intervals indicate that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movements on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. Analyses of stratigraphic intervals above the Morrow indicate that the structural inversion occurred during the Early and Middle Pennsylvanian. The field is regarded as a combination structural-stratigraphic trap. Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado.

Tectonic and Sedimentation Model for Morrow Sandstone Deposition, Sorrento Field Area, Denver Basin, Colorado: ABSTRACT

Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent major Morrow discovery with recoverable reserves estimated at over 10 million bbl of oil from an area of 3,200 ac (1,295 ha.) at depths of 5,400 to 5,600 ft (1,646 to 1,707 m). Minor production also occurs from the Mississippian Spergen and Saint Louis, and the Pennsylvanian Marmaton. Productive Morrow sandstones are interpreted on the basis of subsurface mapping to be fluvial valley-fill deposits, consisting mainly of channel sandstone. These deposits are encased in marine shale and range in thickness from 5 to 55 ft (1.5 to 16.7 m); net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19%, and permeabilities range from 1 to 4,000 md. Isopach maps of the Morrow and associated stratigraphic intervals indicate that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movements on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. Analyses of stratigraphic intervals above the Morrow indicate that the structural inversion occurred during the Early and Middle Pennsylvanian. The field is regarded as a combination structural-stratigraphic trap. Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado. End_of_Article - Last_Page 1319------------

Tectonic and Sedimentation Model for Morrow Sandstone Deposition, Sorrento Field Area, Denver Basin, Colorado: ABSTRACT

Tectonic and Sedimentation Model for Morrow Sandstone Deposition, Sorrento Field Area, Denver Basin, Colorado: ABSTRACT

Sorrento Field--Morrow Discovery in Southeast Colorado: ABSTRACT

Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent Morrow discovery with recoverable reserves estimated at more than 10 million bbl of oil in an area of 3,200 acres (1,280 ha.) at depths of 5,400 to 5,600 ft (1,646 to 1,707 m). Minor production also occurs from the Mississippian Spergen, Mississippian Saint Louis, and Pennsylvanian Marmaton. Productive Morrow sandstones are interpreted on the basis of subsurface mapping as fluvial valley-fill deposits, mainly channel sandstone. These deposits are encased in marine shale and range in thickness from 5 to 55 ft (1.5 to 16.7 m). Net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19% and permeabilities range from 1 to 4,000 md. Analyses of Morrow stratigraphic intervals indicates that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movement on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. The field is regarded as a combination structural-stratigraphic trap. Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado. End_of_Article - Last_Page 530------------

Morrowan Stratigraphy, Depositional Systems, and Hydrocarbon Accumulation, Sorrento Field, Cheyenne County, Colorado: ABSTRACT

The Sorrento field, located on the western flank of the present-day Las Animas arch in western Cheyenne County, Colorado, has approximately 29 million bbl of oil and 12 bcf of gas in place in sandstones of the Lower Pennsylvanian Morrow units. The sandstones were deposited in a fluvially dominated deltaic system, and the trap for the hydrocarbon accumulation is formed by pinch-out of this deltaic system onto regional dip. The primary reservoirs are point-bar deposits. At the Sorrento field, the basal Keyes limestone member of the Morrow formation rests unconformably on the Mississippian St. Louis Formation. Above the Keyes limestone, the Morrow shale is 180 to 214 ft (55 to 65 m) thick, and locally contains reservoir sands. The Morrow shale consists, in ascending order, of: (1) a lower marine shale averaging 40 ft (12 m) thick with minor limestone, siltstone, and sandstone; (2) a deltaic regressive sequence 10 to 65 ft (3 to 20 m) thick consisting of shoreline siltstone that grades laterally into channel-mouth siltstone and sandstone, flood-plain mudstone and coal, fluvial sandstone and conglomerate, levee deposits, and abandoned-channel mudstone; and (3) an upper marine shale averaging 105 ft (32 m) thick with minor limestone and siltstone. The deltaic system prograded from northwest to southeast into a shallow, low-energy sea. The delta was inundated subsequently by regional transgression. The fluvial system of the delta was confined by levees to a meander belt; within this belt, the streams maintained a meandering character to the channel mouth. The major reservoir facies consists of fining-upward grain-size sequences of conglomerate and sandstone up to 55 ft (17 m) thick which are interpreted as point-bar deposits. Individual point bars within the field are characterized by sharp bases, lobate geometry formed by thinning toward the margins due to loss of section from the top, and diameters of 5,200 to 6,500 ft (1,600 to 2,000 m). The bases of the bars consist of very coarse sandstone and granular conglomerate with rip up clasts of shale and coal. Where complete sequences are developed, the bars fine upward to fine-grained sandstone interbedded with shale at the tops. The point bars are overlain by marine shale with little reworking of the upper parts of the bars by marine energy. Channel-mouth bar deposits are developed only locally and are generally silty and tight. One well has encountered reservoir-quality channel-mouth bar sandstone which is distinguished from point-bar sandstone by better sorting, stratigraphic position, and finer grain size lacking the basal, very coarse sandstone and conglomerate. Gas/oil and oil/water contacts are not uniform through the field owing to discontinuities between separate point bars. One such discontinuity is formed by an apparent mud plug of an abandoned channel separating two point bars on the southeastern end of the field. In a well 7,000 ft (2,100 m) from the edge of the meander belt, the regressive sequence is represented by a shoreline siltstone unit 8 ft (2 m) thick with flaser bedding, graded bedding, load structures, and rare wave-ripple cross-bedding overlain by 3 ft (1 m) of flood-plain mudstone and coal with no indication of proximity to a nearby sand system. End_of_Article - Last_Page 1326------------