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Cuttings are an undervalued resource that contain vast amounts of relevant formation evaluation (FE) data in the form of entrained volatile chemistries from present day formation liquids/gases. Analysis of these chemistries in cuttings, or other materials (core, side wall core, and muds), enables decisions from well level completions to acreage/basin assessments on an operational timescale. This work compares analysis of rock volatiles to traditional FE (water saturation and permeability) data to demonstrate correlations to field studies in the Delaware Basin and the STACK. The field study from the SCOOP demonstrates how the analysis can be used to drive completion decisions; studies from the STACK demonstrate how the analysis drove acreage assessment and utilization decisions. All cases are presented from nonhermetically sealed samples showing the applicability of the analysis to fresh or legacy materials.
A unique cryo trap-mass spectrometry (CT-MS) system has been developed by Dr. Michael Smith enabling the gentle extraction of volatiles from cuttings, or other materials, and the subsequent identification and quantification of the extracted chemicals. All possible chemistries (hydrocarbons, organic acids, inorganic acids, noble gases, water, etc.) are extracted by gentle volatilization at room temperature under vacuum conditions and concentrated on a CT; the chemistries are separated by warming the CT and volatilizing as a function of sublimation point and then analyzed by MS. Advantages of this CT-MS over GC-MS are that chemicals that would not survive the conditions of a heated GC system can be analyzed and that the analysis does not require different columns as a function of the species type analyzed. The analysis works on both water and oil based mud systems. These results are combined with a geological interpretation to enable application.
The comparison field studies show that the analysis successfully reproduced Sw and permeability trends from petrophysics and sidewall core analysis. The SCOOP field study identifies the mechanism of underproduction in a Hoxbar well and a simple completion strategy for the lateral that would have significantly reduced costs while enabling equivalent production. The STACK field study was utilized by an operator to evaluate and understand the petroleum system across their acreage and enabled unique acreage utilization decisions in terms of well placement and lateral trajectory.
Copyright 2013, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors This paper was prepared for presentation at the SPWLA 54th Annual Logging Symposium held in New Orleans, Louisiana, June 22-26,2013 ABSTRACT Conventional and Unconventional Gas Resources (CGR, UGR) are a focus area for upstream studies in Saudi Aramco and its Permian clastic reservoirs in particular constitute a world class gas resource. Deposited originally in an Aeolian environment, tight rock partial-seals surround a distribution of permeable "sweet spots". Reservoir development is determined by a complex diagenetic process. The highlighted field is a typical example. During initial appraisal, a continuous gas column was interpreted from pre-production pressure data with a clear free water level. Yet, as development progressed, development wells encountered water up structure and pressure depletion showed a complex pseudo-compartmentalization, in contradiction of the initial model assumptions. As part of ongoing reservoir management, an extensive special core analysis program has been conducted on a comprehensive set of some 300 samples encompassing the range in rock quality present in the formation which ranged from highly permeable quartz rich dunes to diagenetically altered paleosols, siltstones and shales.The bulk of samples showed meso-and macro-pore structures typical of silt to clean sandstone dominated rock sequences. This is interesting because although these rock types should be filled with gas, given the expected column height of approximately 1000 ft, none of the rocks examined showed a gas sealing potential of more than a few hundred feet.
This paper summarizes the comprehensive reservoir characterization effort for the foam pilot area and discusses the response to foam injection in the CO2 Foam Field Verification Pilot Test conducted in the East Vacuum Grayburg San Andre S Unit (EVGSAU) in New Mexico. A detailed study of the pilot pattern geology provided an understanding of the major controls on fluid flow in the foam pattern. Pattern performance data, falloff testing, profile surveys, and interwell tracer results were integrated into the geologic model to guide project design work and provide a framework for interpretation of foam performance. Localized regions of high permeability resulting from solution enhancement of the matrix pore system appear to be the primary cause of the early CO2 breakthrough and channeling of injected CO2 toward the problem production well in the foam pattern. Positive response to foam injection is indicated by reduced injectivity and injection profile data in the foam injection well; by results from time sequence monitor logging in the observation well; and by changes in production performance in the high GOR, "offending" production well in the foam pattern. Hall plots and pressure falloff testing were used to measure in situ changes in fluid mobility near the foam injection well. Time sequence logging responses at an observation well located 150 feet from the foam injector provided evidence of changes in fluid flow patterns in response to foam injection. Positive response to foam injection is further evidenced by changes in the CO2 production and oil rate performance at the "offending" production well in the foam pilot pattern.
EVGSAU GEOLOGIC SETTING
The Vacuum Field, located about 15 miles northwest of Hobbs in Lea County, New Mexico, is comprised of several large Units and leases. The East Vacuum Grayburg-San Andres Unit (EVGSAU) covers more than 7000 acres on the eastern side of the Vacuum Field. The primary productive interval at EVGSAU is comprised of the dolomitized carbonate sequences in the upper few hundred feet of the San Andres Formation, at a depth of approximately 4500 feet. The San Andres structure is an east-west trending anticline with more than 400 feet of closure above the original oil/water contact. The reservoir section is informally subdivided into a "lower" San Andres section and an "upper" San Andres section, separated by the more siliciclastic Lovington Sandstone Member.
Stratigraphy and Lithofacics
The San Andres reservoir section is comprised of a series of repeated, anhydritic, dolomitized, fining-upward, carbonate sequences composed of grain-rich dolostones which grade upward into dolomudstones. The subtidal, grain-rich carbonate facies form the primary reservoir units; the dolomudstones contain little effective porosity. Repetition of these depositional packages upwards through the formation results in a San Andres section composed of cyclical, shallowing/shoalingupward parasequences. Commonly occurring reservoir pore types include primary intergranular porosity, intercrystalline porosity (related to dolomitization), grain-moldic porosity, and vugular porosity. All of these pore types show varying degrees of solution enhancement.