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Title: Evaporite geometries and diagenetic traps, lower San Andres, Northwest shelf, New Mexico

Abstract

An east-west-trending belt of lower San Andres oil fields extends 80 mi across southeastern New Mexico from the Pecos River near Roswell to the Texas-New Mexico border. These fields are along a porosity pinch-out zone where porous carbonates grade laterally into bedded anhydrite and halite. The lower San Andres traps are associated with pre-Tertiary structural or stratigraphic traps. Oil and water production relationships from these fields are not consistent with present-day structure. These fields have been commonly interpreted to be hydrodynamic traps created by the eastern flow of fresh surface water that enters the lower San Andres outcrops west of Pecos River. There is no evidence, however, that surface water has moved through the lower San Andres in this area. This conclusion is supported by the fact that formation-water resistivities are uniform throughout the producing trend, no significant dissolution of carbonates or evaporites has occurred, and there has been no increase in biogradation of oils adjacent to the lower San Andres outcrops. These fields actually are diagenetic traps created by porosity occlusion in the water column beneath the oil accumulations. Hydrocarbons originally were trapped in pre-Tertiary structural and structural-stratigraphic traps. Bedded evaporites were effective barriers to vertical and lateral hydrocarbonmore » migration. Eastward tilting of the Northwest shelf during the Tertiary opened these traps, but the oil remained in these structurally unfavorable positions because of the diagenetic sealing. The gas-solution drive in these reservoirs is a result of this sealing. The sequence of events leading to diagenetic entrapment include (1) Triassic and Jurassic migration of hydrocarbons into broad, low-relief post-San Andres structural and structural-stratigraphic traps; (2) rapid occlusion of porosity in the water column beneath oil reservoirs, and (3) Tertiary tilt-out traps.« less

Authors:
 [1]
  1. (Chevron USA, Midland, TX (United States))
Publication Date:
OSTI Identifier:
7195620
Report Number(s):
CONF-9204139--
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States); Journal Volume: 76:4; Conference: American Association of Petroleum Geologists (AAPG) Southwest section meeting, Midland, TX (United States), 21-24 Apr 1992
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; NEW MEXICO; PETROLEUM DEPOSITS; DIAGENESIS; GEOLOGIC TRAPS; DISSOLUTION; EVAPORITES; PETROLEUM GEOLOGY; POROSITY; RESERVOIR ROCK; STRATIGRAPHY; DEVELOPED COUNTRIES; FEDERAL REGION VI; GEOLOGIC DEPOSITS; GEOLOGY; MINERAL RESOURCES; NORTH AMERICA; RESOURCES; ROCKS; SEDIMENTARY ROCKS; USA 020200* -- Petroleum-- Reserves, Geology, & Exploration

Citation Formats

Keller, D.R. Evaporite geometries and diagenetic traps, lower San Andres, Northwest shelf, New Mexico. United States: N. p., 1992. Web.
Keller, D.R. Evaporite geometries and diagenetic traps, lower San Andres, Northwest shelf, New Mexico. United States.
Keller, D.R. 1992. "Evaporite geometries and diagenetic traps, lower San Andres, Northwest shelf, New Mexico". United States. doi:.
@article{osti_7195620,
title = {Evaporite geometries and diagenetic traps, lower San Andres, Northwest shelf, New Mexico},
author = {Keller, D.R.},
abstractNote = {An east-west-trending belt of lower San Andres oil fields extends 80 mi across southeastern New Mexico from the Pecos River near Roswell to the Texas-New Mexico border. These fields are along a porosity pinch-out zone where porous carbonates grade laterally into bedded anhydrite and halite. The lower San Andres traps are associated with pre-Tertiary structural or stratigraphic traps. Oil and water production relationships from these fields are not consistent with present-day structure. These fields have been commonly interpreted to be hydrodynamic traps created by the eastern flow of fresh surface water that enters the lower San Andres outcrops west of Pecos River. There is no evidence, however, that surface water has moved through the lower San Andres in this area. This conclusion is supported by the fact that formation-water resistivities are uniform throughout the producing trend, no significant dissolution of carbonates or evaporites has occurred, and there has been no increase in biogradation of oils adjacent to the lower San Andres outcrops. These fields actually are diagenetic traps created by porosity occlusion in the water column beneath the oil accumulations. Hydrocarbons originally were trapped in pre-Tertiary structural and structural-stratigraphic traps. Bedded evaporites were effective barriers to vertical and lateral hydrocarbon migration. Eastward tilting of the Northwest shelf during the Tertiary opened these traps, but the oil remained in these structurally unfavorable positions because of the diagenetic sealing. The gas-solution drive in these reservoirs is a result of this sealing. The sequence of events leading to diagenetic entrapment include (1) Triassic and Jurassic migration of hydrocarbons into broad, low-relief post-San Andres structural and structural-stratigraphic traps; (2) rapid occlusion of porosity in the water column beneath oil reservoirs, and (3) Tertiary tilt-out traps.},
doi = {},
journal = {AAPG Bulletin (American Association of Petroleum Geologists); (United States)},
number = ,
volume = 76:4,
place = {United States},
year = 1992,
month = 4
}

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  • The Permian basin of southeastern New Mexico and west Texas has historically been one of the most productive areas for the discovery and exploitation of hydrocarbons in North America. Exploration methods in this area have included various methods of subsurface mapping, primarily structural mapping, often used in conjunction with seismic interpretation. These techniques have accounted for all the oil discovered to date in the Permian basin. Because most of the easily discovered oil has been found, the old techniques may have reached their limit of usefulness. A technique developed by Scholten is amplified and applied to identifying the so-called subtlemore » trap in the Delaware basin and Northwest shelf of New Mexico. The technique uses well-log-derived mapping intervals to identify paleostructures into which hydrocarbons migrated simultaneously with or immediately after formation of the structures. Regionally thin areas in the mapping have been identified as ancient geologic structures into which hydrocarbons migrated simultaneously with or immediately after formation of the structures. Regionally thin areas in the mapping have been identified as ancient geologic structures into which hydrocarbons have migrated. This study found a greater than 85% correlation between one or more pay horizons per map interval and economic production in several distinct geologic provinces in which the technique was used. Several examples from various fields in southeastern New Mexico include different pay horizons, both shallow and deep, in clastic and carbonate rocks. Observations are also made on the regional geology and stratigraphy of the southeastern New Mexico area.« less
  • Superb exposures of variably cyclic, fusulinid-rich, outer ramp facies of the middle San Andres Formation in the Guadeloupe Mountains, NM provide a unique opportunity to evaluate spatial variability of permeability and its relationship to depositional and diagenetic fabric. Detailed geologic description and extensive permeability measurements have been utilized to decipher reservoir-analog flow units and the spatial variability of observed permeability patterns. Thin bedded, poorly developed cycles consisting of alternating fusulinid-peloid dolopackstones and dolowackestones occur within the middle portion of the middle San Andres. Four well developed cycles or parasequences containing dolomudstone bases and fusulinoid-peloid dolopackstone tops comprise the upper portionmore » of the middle San Andres. Upward increasing trends in permeability are evident within each of the well developed cycles whereas a distinct 30 foot thick zone of highly variable but higher mean permeability occurs within the poorly developed thin bedded cycles. Textural characteristics were compared with conventional air permeabilities. Statistically different mean permeabilities are related to variation of grain, matrix, fusulinid mold, and vug content. Permeability is also related to the abundance of white sucrosic dolomite, which appears to have inhibited the development of fusulinid moldic porosity. Based on these relationships, more accurate permeability transforms may be developed and used to map permeability distribution in similar facies within reservoirs. Geostatistical analysis of the permeability populations and within-cycle permeability trends indicate an association to facies and diagenetic-zone dimensions both vertically and laterally. Ranges of correlation support a nearly uncorrelated and highly-variable permeability model within fusulinid-rich cycles of a ramp-carbonate setting.« less
  • The Permian San Andres Formation was deposited in environments ranging from supratidal to subtidal, protected shallow marine to open shallow marine. Pelletoid-skeletal packstone/wackestone and pelletoid-oolite-skeletal packstone/grainstone facies of the composite subtidal, marine environments were concentrated in the southern half of the field where grainstone deposition was linked to a paleotopographic high. Deposition in the northern half of the field was dominated by the pelletoid wackestone/mudstone facies of the supratidal, restricted shallow-marine environment. Porosity is mainly diagenetic in origin. San Andres rocks passed through the marine phreatic, the mixed phreatic, the meteoric phreatic, and the deeper subsurface diagenetic environments. Matrix dolomitizationmore » in the marine and mixed-phreatic environment produced intercrystalline porosity in all the facies. Leaching of nondolomitized grains in the mixed phreatic and meteoric-phreatic environments created large moldic pores. Diagenetic patterns follow structural and depositional trends so that suites of characteristic pore types exist for each facies. Individual pore types consist of moldic, intergranular, intragranular, vuggy, and intercrystalline categories. Intercrystalline pores are present nearly everywhere, and predicting the abundance of moldic pores is the largest variable in predicting porosity values for a given stratigraphic interval. Highest porosity exists in the southern half of the study area where grainier facies were deposited on a paleotopographic high, and grains were partly dolomitized and subsequently were removed by leaching, leaving behind a composite intercrystalline-moldic pore network. Total porosity values do not correspond with facies boundaries, so porosity mapping was accomplished by dividing the San Andres into 20-ft-thick slices and computer contouring total porosity greater than 6% in each slice.« less
  • The San Andres Formation of Permian age (late Leonardian-early Guadalupian) is the most prolific producer of hydrocarbons within the Permian basin. The Levelland-Slaughter trend, located in the northwestern shelf province, is a series of east-west-trending fields characterized by stratigraphically controlled, updip porosity pinchouts from porous dolomites to nonporous dolomites and evaporites. Equivalent facies crop out in Chaves and Lincoln Counties, New Mexico. Outcrop study and examination of subsurface data from shallow pay zones within the Diablo, Linda, and Twin Lakes fields, indicate that a variety of high- and low-energy subtidal facies serve as reservoirs. These include (1) oolite packstones andmore » grainstones, (2) wispy-laminated crinoid wackestones, (3) fossiliferous wackestones, and (4) ripple-laminated pellet grainstones. These facies were deposited as a mosaic in channels, lagoons, shoals, and shallow open-marine environments. Vertical and lateral facies relationships are therefore highly variable and play a major role in reservoir heterogeneity. Secondary porosity is wholly responsible for oil production, although the depositional setting controls its type and abundance. Intercrystalline porosity is characteristic of the mud-rich facies and is crucial for economic production. Sucrosic textures associated with coarse crystalline dolomite and large intercrystalline pores provide the highest production potential. Moldic porosity is characteristic of the oolitic and fossiliferous facies, but pores are disconnected and only marginally productive unless combined with fractures.« less
  • Outcrop exposures of Permian San Andres dolomites were examined in the Guadalupe Mountains of southeastern New Mexico to gain insight into the lateral continuity of permeable, reservoir-quality beds. The investigation focused on the continuity that can be expected between an injector and producer on 40-ac spacing or 1,320 ft. The exposed rocks closely resemble subsurface producing strata, both in their regional setting on a broad carbonate shelf and in their detailed petrographic and petrophysical properties. Weathering of the outcrop is not so severe as to invalidate the conclusions. Individual beds were sampled at intervals of 100 ft, 10 ft betweenmore » selected 100-ft intervals, and 1 ft or less between selected 10-ft stations. More than 1,000 permeability plugs were analyzed. Permeable beds are found in the middle of the San Andres section starting about 350 ft below the top of the San Andres Formation. The middle and upper sections of the San Andres are well bedded, abrupt lateral facies changes were not found. Beds with pay-type permeability are interbedded with laterally continuous impermeable mudstone that should act as effective barriers to crossflow. All permeable beds would have to be perforated to drain or flood this type of reservoir effectively. Permeability within a given reservoir bed is highly variable, with the range of values averaging three orders of magnitude and the standard deviation averaging one order of magnitude. This range is present irrespective of the sampling interval. The pay-quality rock appears continuous on the 40-ac scale within any of the reservoir beds. The permeability path is tortuous, however, suggesting that oil could be trapped or bypassed in low-permeability pockets or reentrants.« less