Temblor Formation Research Articles

Strategies for hydrogen storage in a depleted sandstone reservoir from the San Joaquin Basin, California (USA) based on high-fidelity numerical simulations

Depleted hydrocarbon reservoirs are promising candidates for underground hydrogen (H2) storage (UHS) due to their known (and often high) storage capacity, well-identified geological conditions, reduced cushion gas requirements, and adaptable existing infrastructure. While these reservoirs have shown success in natural gas storage, their performance for pure H2 storage remains untested, necessitating further research. To address this knowledge gap, we conduct high-fidelity multiphase compositional reservoir simulations to evaluate the technical feasibility of UHS in a depleted hydrocarbon reservoir within the Temblor Formation at the North Belridge Field from the San Joaquin Basin, California, USA. This reservoir zone comprises five distinct sand layers separated by four shale intervals and is bounded above and below by thick shales (overburden and underburden, respectively). This research has two primary objectives: (a) to assess the feasibility of two distinct UHS strategies—one that involves storing H2 across all sand layers and another that stores an equal amount of H2 in the single thickest sand layer, and (b) to evaluate the effect of interbedded shale permeability on UHS performance. Our findings indicate that UHS in the Temblor Formation is technically viable, showing enhanced H2 withdrawal efficiency and produced H2 purity over successive cycles with minimal leakage risk. The two storage strategies significantly impact UHS performance in the interbedded sandstone sequence. Storing H2 across all sand layers results in higher H2 withdrawal efficiency, but lower produced H2 purity. In contrast, storing H2 in a single sand layer leads to lower withdrawal efficiency but consistently high H2 purity. In addition, H2 storage in a single sand layer results in higher reservoir pressure buildup, implying greater geomechanical risks. The impact of interbedded shale permeability on UHS performance is negligible across the range of uncertainty for shale permeability. This research not only lays the groundwork for potential UHS implementation in the abundant sandstones of the San Joaquin Basin of California, but also offers valuable insights for other depleted hydrocarbon reservoirs under consideration for UHS that share similar properties.

Stable isotope evidence for resource partitioning in extinct marine carnivores

Living pinnipeds play essential roles in marine ecosystems and display divergent lineage-specific foraging and habitat preferences. The origin of these ecological strategies remains unclear. We analyzed original (n = 22) and published (n = 93) stable carbon (δ13C) and oxygen (δ18O) isotope compositions of tooth enamel from fossil pinnipeds and coeval marine and terrestrial mammals from the late Early Miocene to early Middle Miocene Temblor Formation, the early Middle Miocene Round Mountain Silt Formation at Sharktooth Hill Bonebed, the Middle Miocene of lower levels of the Monterey Formation, and the late Middle Miocene Santa Margarita Formation from the eastern North Pacific Ocean; and original (n = 43) δ13C and δ18O values from the Early Pliocene Yorktown Formation in the western North Atlantic. As expected for aquatic mammals, pinnipeds and control marine mammals had low δ18O variability relative to coeval terrestrial mammals, indicating minimal diagenetic alteration. Among late Early Miocene and Middle Miocene pinnipeds, Allodesmus had lower δ13C values than coeval taxa indicating offshore foraging, in agreement with predictions based on skeletal morphology. However, Allodesmus from the late Middle Miocene Santa Margarita Formation had overlapping δ13C values with co-occurring cetaceans and pinnipeds suggesting preferential nearshore habitat. The stem otariid Pithanotaria had higher enamel δ13C values than co-occurring pinnipeds, indicating nearshore foraging. The stem odobenid Neotherium had intermediate δ13C values supporting foraging between nearshore and offshore predators. Conversely, the stem odobenid cf. Imagotaria had lower enamel δ18O but comparable δ13C values to coexisting pinnipeds, suggesting the exploitation of estuarine resources. At least two ecologically distinct pinniped groups also occurred in the Yorktown Formation. In this unit, the odobenid Ontocetus and some monachinae phocids were predominantly nearshore foragers, with higher enamel δ13C and δ18O values than simultaneously occurring marine mammals. The second group was exclusively composed of phocids, which had comparatively low δ13C and δ18O values, compatible with northward foraging movements along the western North Atlantic coast. The paleoecological profiles of fossils bear strong similarities to the life modes of extant pinniped communities, implying that extant foraging modes appeared early in pinniped evolution and that resource partitioning contributed to their community structure over time.

New remains of middle Miocene equids from the Cajon Valley Formation, San Bernardino National Forest, San Bernardino County, California, USA

New material of three equids is described from the middle Miocene Cajon Valley Formation in San Bernardino National Forest, San Bernardino County, California. The material includes teeth of Archaeohippus mourningi, Scaphohippus sumani, and Parahippus brevidens. Scaphohippus intermontanus is considered a junior subjective synonym of S. sumani. Parahippus brevidens is identified from an upper molar that closely resembles the morphology of the holotype as well as referred specimens of Pa. brevidens from the Mascall Formation in Oregon and the Temblor Formation in California. The presence of Pa. brevidens in the Cajon Valley Formation represents a geographic range extension for the taxon of over 400 km. Interesting ecological implications emerge for the Cajon Valley Formation when compared to the nearby Barstow Formation, including the presence of chalicotheres and apparent lack of Hypohippus affinis and Megahippus mckennai.

Reconciling along-strike disparity in slip displacement of the San Andreas fault, central California, USA

Abstract The correlation of the ca. 23 Ma Pinnacles and Neenach volcanic complexes provides the most robust estimate on the timing and magnitude of Neogene right-lateral displacement on the San Andreas strike-slip fault system (California, United States). Displacement of ∼315 km has been applied rigorously along the plate margin to guide reconstruction of offset paleogeographic features. We present new detrital zircon U-Pb geochronology from the La Honda and western San Joaquin basins to document sediment provenance and reevaluate compositional constraints on a hypothesized key cross-fault tie (i.e., Castle Rock–Recruit Pass submarine fan system). Whereas the Upper Oligocene–Lower Miocene Vaqueros Formation of the La Honda basin was likely recycled from or shared a similar southern Sierra Nevada–western Mojave source with the underlying Eocene stratigraphy, we found that the Temblor Formation of the central Temblor Range (e.g., Recruit Pass submarine fan) was derived directly from Late Cretaceous northern Salinian basement. Furthermore, the Carneros Sandstone of the northern Temblor Range had a central Sierra Nevada batholith source that was likely recycled during early Miocene unroofing of the underlying stratigraphy. Conversely, strata of the southwest San Joaquin basin have provenance characteristics that match more closely with those of the La Honda basin. Our data preclude a contiguous Castle Rock–Recruit Pass submarine fan system across the San Andreas fault. These relationships are resolved by restoring the ca. 105–100 Ma basement of the northernmost Salinian block an additional ∼45 km or greater farther south relative to the Sierra Nevada batholith during late Oligocene–early Miocene time. Inconsistency in displacement along the San Andreas fault with the coeval correlation of the Pinnacles–Neenach volcanic complex is reconciled by postdepositional Miocene–Quaternary off-fault NW-SE structural shortening via major thrusts and/or transrotation of the Tehachapi block, in combination with extension of the northern Salinian block. This additional displacement reduces the need for pre–28 Ma slip on the San Andreas or predecessor faults to resolve Cretaceous through Eocene cross-fault relationships and reconciles an early Miocene discrepancy with Pacific–North America relative plate motion. This study highlights the fact that displacement histories of major strike-slip faults are divergent across changing structural domains, and recognition of slip disparities can constrain the magnitude of deformation.

New data on the early odobenid Neotherium mirum Kellogg, 1931, and other pinniped remains from the Sharktooth Hill Bonebed, California

Deposited over a short period of time during the Middle Miocene Climatic Optimum, the Sharktooth Hill Bonebed in California is one of the world’s densest marine vertebrate concentrations. Pinnipeds are represented here by odobenids and desmatophocids, but some are still poorly known. Herein, the mandibular morphology of the odobenid Neotherium mirum is described in detail. Its morphology resembles that of early pinnipedimorphs, with postcanine teeth consisting of three or four longitudinally aligned cusps and double-rooted p2–m1, but shows derived characteristics such as reduced metaconid and bilobed canine root. Additionally, Neotherium is represented by two distinct size classes, which is likely the earliest evidence of sexually dimorphic body size in odobenids. Two additional mandibles represent other pinnipeds. One represents an unknown odobenid, with a unique suite of morphological characteristics setting it apart from contemporaneous odobenids such as Neotherium and Pelagiarctos. The other reconfirms the presence of Allodesmus cf. A. sadoensis, a species otherwise known from the middle Miocene of Japan. This species is distinguished from Allodesmus kernensis, based on anteriorly crowded and reduced postcanine dentition. This record adds further support for the presence of this taxon in the middle Miocene of California and represents the earliest evidence of trans-Pacific dispersal in pinnipeds. The Sharktooth Hill pinniped assemblage now consists of five species: the odobenids Neotherium mirum, Pelagiarctos thomasi, an unknown odobenid, and the desmatophocids Allodesmus kernensis and Allodesmus cf. A. sadoensis. Niche partitioning within this sympatric pinniped community was possible due to differences in body size, and feeding and foraging preferences.

Eotaria citrica, sp. nov., a new stem otariid from the "Topanga" formation of Southern California.

A new taxon of stem otariid, Eotaria citrica sp. nov., is described from the upper Burdigalian to lower Langhian “Topanga” formation of Orange County, California. The new species is described from mandibular and dental remains that show a unique combination of plesiomorphic and derived characters. Specifically, it is characterized by having trenchant and prominent paraconid cusps in p3–m1, lingual cingula of p2–4 with faint crenulations, premolars and molars with vestigial metaconid, bilobed root of m2 and a genial tuberosity located under p3. Furthermore, additional material of the contemporaneous Eotaria crypta is described, providing new information on the morphology of this taxon. Both species of Eotaria represent the earliest stem otariids, reinforcing the hypothesis that the group originated in the north Eastern Pacific Region. At present, the “Topanga” Fm. pinniped fauna includes Eotaria citrica, Eotaria crypta, the desmatophocid Allodesmus sp., the odobenids Neotherium sp., Pelagiarctos sp. and includes the oldest records of crown pinnipeds in California. Overall this pinniped fauna is similar to the nearly contemporaneous Sharktooth Hill bonebed. However, unambiguous records of Eotaria are still missing from Sharktooth Hill. This absence may be due to taphonomic or paleoenvironmental factors. The new “Topanga” record presented here was integrated into an overview of the late Oligocene through early Pleistocene pinniped faunas of Southern California. The results show an overall increase in body size over time until the Pleistocene. Furthermore, desmatophocids were the largest pinnipeds during the middle Miocene, but were extinct by the beginning of the late Miocene. Odobenids diversified and became the dominant pinnipeds in late Miocene through Pleistocene assemblages, usually approaching or exceeding 3 m in body length, while otariids remained as the smallest taxa. This pattern contrasts with modern assemblages, in which the phocid Mirounga angustirostris is the largest pinniped taxon in the region, odobenids are extinct and medium and small size ranges are occupied by otariids or other phocids.

Carbon storage and CO2-enhanced oil recovery potential in the Temblor Formation, northeast McKittrick oilfield, San Joaquin Valley, California

Net fluid production and pressure data were gathered to estimate the amount of storage space available and the potential for additional oil recovery using -enhanced oil recovery (EOR) in the Phacoides sandstone, McKittrick oilfield, San Joaquin Valley, California. The Phacoides reservoir has produced 61.5 million reservoir barrels of fluid, a volume equivalent to the subsurface capacity of 9.8 million metric tons of . Reservoir pressure changes with fluid production suggest that injecting 1 million metric tons of may raise reservoir pressures by 2 MPa (255 psi). We assume that the sealing capacity of the reservoir for injection is equivalent to the conditions controlling the original hydrocarbon accumulation. If injection pressures exceed this limit, the could leak through the caprock, from aging wellbores or along faults in the reservoir. Faulting has compartmentalized the reservoir into six major blocks with varying degrees of hydraulic communication. Injection wells will be required within each sealed fault block, resulting in additional costs for implementing a carbon capture and sequestration (CCS) project. Through -EOR, an additional 17 million bbl of oil may be recoverable, thereby offsetting the cost of carbon storage. This is equivalent to 1.4 million metric tons of additional storage space. However, assuming that none of the carbon is captured, combustion of this additional oil will add approximately 7 million metric tons of to the atmosphere, negating the available storage space in the reservoir and resulting in a net carbon gain to the atmosphere of 700,000 metric tons.

Combining forces--the use of Landsat TM satellite imagery, soil parameter information, and multiplex PCR to detect Coccidioides immitis growth sites in Kern County, California.

Coccidioidomycosis is a fungal disease acquired through the inhalation of spores of Coccidioides spp., which afflicts primarily humans and other mammals. It is endemic to areas in the southwestern United States, including the San Joaquin Valley portion of Kern County, California, our region of interest (ROI). Recently, incidence of coccidioidomycosis, also known as valley fever, has increased significantly, and several factors including climate change have been suggested as possible drivers for this observation. Up to date details about the ecological niche of C. immitis have escaped full characterization. In our project, we chose a three-step approach to investigate this niche: 1) We examined Landsat-5-Thematic-Mapper multispectral images of our ROI by using training pixels at a 750 m×750 m section of Sharktooth Hill, a site confirmed to be a C. immitis growth site, to implement a Maximum Likelihood Classification scheme to map out the locations that could be suitable to support the growth of the pathogen; 2) We used the websoilsurvey database of the US Department of Agriculture to obtain soil parameter data; and 3) We investigated soil samples from 23 sites around Bakersfield, California using a multiplex Polymerase Chain Reaction (PCR) based method to detect the pathogen. Our results indicated that a combination of satellite imagery, soil type information, and multiplex PCR are powerful tools to predict and identify growth sites of C. immitis. This approach can be used as a basis for systematic sampling and investigation of soils to detect Coccidioides spp.

A new fossil basking shark (Lamniformes: Cetorhinidae) from the Middle Miocene Sharktooth Hill bonebed, Kern County, California

A new fossil basking shark (Lamniformes: Cetorhinidae) from the Middle Miocene Sharktooth Hill bonebed, Kern County, California

A reevaluation of the morphology, paleoecology, and phylogenetic relationships of the enigmatic walrus Pelagiarctos.

BackgroundA number of aberrant walruses (Odobenidae) have been described from the Neogene of the North Pacific, including specialized suction-feeding and generalist fish-eating taxa. At least one of these fossil walruses has been hypothesized to have been a specialized predator of other marine mammals, the middle Miocene walrus Pelagiarctos thomasi from the Sharktooth Hill Bonebed of California (16.1–14.5 Ma).Methodology/Principal FindingsA new specimen of Pelagiarctos from the middle Miocene “Topanga” Formation of southern California (17.5–15 Ma) allows a reassessment of the morphology and feeding ecology of this extinct walrus. The mandibles of this new specimen are robust with large canines, bulbous premolars with prominent paraconid, metaconid, hypoconid cusps, crenulated lingual cingula with small talonid basins, M2 present, double-rooted P3–M1, single-rooted P1 and M2, and a P2 with a bilobate root. Because this specimen lacks a fused mandibular symphysis like Pelagiarctos thomasi, it is instead referred to Pelagiarctos sp. This specimen is more informative than the fragmentary holotype of Pelagiarctos thomasi, permitting Pelagiarctos to be included within a phylogenetic analysis for the first time. Analysis of a matrix composed of 90 cranial, dental, mandibular and postcranial characters indicates that Pelagiarctos is an early diverging walrus and sister to the late Miocene walrus Imagotaria downsi. We reevaluate the evidence for a macropredatory lifestyle for Pelagiarctos, and we find no evidence of specialization towards a macrophagous diet, suggesting that Pelagiarctos was a generalist feeder with the ability to feed on large prey.Conclusions/SignificanceThis new specimen of Pelagiarctos adds to the knowledge of this problematic taxon. The phylogenetic analysis conclusively demonstrates that Pelagiarctos is an early diverging walrus. Pelagiarctos does not show morphological specializations associated with macrophagy, and was likely a generalist predator, feeding on fish, invertebrates, and the occasional warm-blooded prey item.

Chemometric differentiation of crude oil families in the San Joaquin Basin, California

Chemometric analyses of geochemical data for 165 crude oil samples from the San Joaquin Basin identify genetically distinct oil families and their inferred source rocks and provide insight into migration pathways, reservoir compartments, and filling histories. In the first part of the study, 17 source-related biomarker and stable carbon-isotope ratios were evaluated using a chemometric decision tree (CDT) to identify families. In the second part, ascendant hierarchical clustering was applied to terpane mass chromatograms for the samples to compare with the CDT results. The results from the two methods are remarkably similar despite differing data input and assumptions. Recognized source rocks for the oil families include the (1) Eocene Kreyenhagen Formation, (2) Eocene Tumey Formation, (3–4) upper and lower parts of the Miocene Monterey Formation (Buttonwillow depocenter), and (5–6) upper and lower parts of the Miocene Monterey Formation (Tejon depocenter). Ascendant hierarchical clustering identifies 22 oil families in the basin as corroborated by independent data, such as carbon-isotope ratios, sample location, reservoir unit, and thermal maturity maps from a three-dimensional basin and petroleum system model. Five families originated from the Eocene Kreyenhagen Formation source rock, and three families came from the overlying Eocene Tumey Formation. Fourteen families migrated from the upper and lower parts of the Miocene Monterey Formation source rocks within the Buttonwillow and Tejon depocenters north and south of the Bakersfield arch. The Eocene and Miocene families show little cross-stratigraphic migration because of seals within and between the source rocks. The data do not exclude the possibility that some families described as originating from the Monterey Formation actually came from source rock in the Temblor Formation.

New observations on the Middle Fork Eel River coal-bearing beds, Mendocino County, California, USA

Mid-19th century reports of “immense” coal outcrops in the Middle Fork Eel River (MFER) drainage near Round Valley in California's northern Coast Ranges fueled the early geological interest in this area, with mine development the primary focus of many studies. It was not until Samuel G. Clark's 1940 “Geology of the Covelo District, Mendocino County, California,” that the coal was placed in its regional geologic context and assigned to the Miocene, a determination that relied primarily on a Desmostylus hesperus molar found in shale overlying the coal and an associated equivocal, though Miocene-compatible, marine molluscan fauna. Our investigation of the MFER coal-bearing beds has provided new data from foraminifera, marine mollusks, fish remains, and the first reported fossil plants, which as a whole support Clark's Miocene age assignment. We also present an updated stratigraphy proposing under modern-day stratigraphic protocols that the informal name Sand Bank beds (SBb) be used in place of the Temblor Formation to refer to the SBb coal-bearing fluvial-marine unit. Analysis of the SBb stratigraphy and sedimentology reveals the presence of a fluvial system that flowed from a distal upland region southward toward the paleocoast of California. An abundant diverse palynoflora containing lycophytes, ferns, conifers, and mesic, thermophillic herbaceous and woody angiosperms indicates the drainage flowed through a coastal swampy forested bottomland and estuarine environment before emptying into a coastal basin. Presence of Taxodium-like wood, foliage, pollen, and other “hydrophiles” suggests the MFER coal was a local mire buried by the progradation of the SBb fluvial system during a regressive phase, an interpretation to be tested with future field work and detailed compositional analysis of the coal.

A new immigrant mustelid (Carnivora, Mammalia) from the middle Miocene Temblor Formation of central California

A new mustelid genus from the Barstovian (middle Miocene) marine Temblor Formation in California is described. The material of Legionarictis fortidens includes an incomplete cranium with partial upper dentition. The straight lingual border and slightly expanded posterointernal cingulum of M1 are plesiomorphic traits, as in the European Dehmictis. However, the M1 is not as posteriorly expanded, and the P4 does not have a lingual hypoconal crest, differentiating L. fortidens from younger North American forms. Furthermore, the P4 protocone is posteriorly placed from the parastyle crest, as in the extant South American Eira. An autapomorphic feature of L. fortidens is its highly hypertrophied P4 paracone with a bulbous crown. The robust upper carnassial, very strong development of the sagittal crest, and derived enamel microstructure all suggest a hard food component in its diet. The coastal depositional environment indicated by the presence of marine taxa in the Temblor Formation suggests that hard shelled invertebrates might have been a food source of L. fortidens. A combination of plesiomorphic and derived dental characteristics puts the new form at an evolutionary stage basal to otters and closer to the living Eira. Cladistic analysis of craniodental characters suggests that L. fortidens is more derived than generalized basal mustelines of the Old World, and may have diverged from the lutrine lineage in a separate immigration event to the New World.

Origin of a widespread marine bonebed deposited during the middle Miocene Climatic Optimum

Bonebeds are vertebrate bioclast concentrations in beds that are local to basinal in extent. The middle Miocene Sharktooth Hill bonebed in the southeastern San Joaquin Basin of California is among the largest of such deposits, exposed over 15 km and containing a rich assemblage of marine vertebrates, with a mean density of ~200 specimens/m 2 . It ranks among the most widespread and richest bonebeds known, yet its genesis is poorly understood. Hypotheses for its origin and formation include mass death from shark predation, volcanic or red tide poisoning, accumulation from a calving ground for marine mammals, and condensed accumulation over a long period of time. Based on multiple kinds of evidence, we conclude that the bonebed formed over a protracted time interval of little to no net clastic sedimentation, coincident with a significant transgressive-regressive cycle between 16 and 15 Ma ago, during the middle Miocene Climatic Optimum (MMCO). Geochronological constraints bracket the duration of bonebed formation to no longer than 700 ka, indicating that time averaging is a critical consideration for paleoecological analyses of North Pacific Ocean biotic richness during the MMCO.

Field Surveillance and Well-Services Management in a Large Mature Onshore Field

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 99949, "Real-Time Field Surveillance and Well-Services Management in a Large Mature Onshore Field: Case Study," by L. Ormerod, SPE, Weatherford; H. Sardoff, SPE, J. Wilkinson, SPE, and B. Erlendson, Chevron; and B. Cox and G. Stephenson, SPE, Weatherford, prepared for the 2006 SPE Intelligent Energy Conference and Exhibition, Amsterdam, 11–13 April. A real-time field-surveillance and well-services management system was deployed in an onshore mature field in California. The challenges of data management included automatic handling of very large quantities of real-time data, management of inventory, and integration of field-level data with corporate-level data. Technologies required for this project included software systems and integration of these with remote intelligent-field sensors and data-transmission systems. This project established that integrated intelligent remote devices, communications networks, and workflow-management software could be deployed successfully on large mature fields. Prior State of the Business Chevron's San Joaquin Valley Business Unit (SJVBU) is in the southern San Joaquin Valley in central California. The SJVBU operations encompass assets in seven oil fields, which before the merger of Chevron and Texaco were operated by those two companies. The earliest of these oil fields was developed in the early 1900s. Most of the development occurred in the 1960s and 1970s with the implementation of steamflood technology. Aggregate production from the SJVBU assets is approximately 200,000 BOPD. Approximately 15,000 active wells produce in the SJVBU, yielding an average production of approximately 13 BOPD/well. The SJVBU fields produce from relatively shallow reservoirs, including the Miocene/Pliocene Kern River, Tulare, Temblor, and Potter formations, which typically have porosities ranging from 20 to 30% and permeability in the range of 1 to 5 md. Oil gravity ranges from 13 to 20°API, and viscosity is approximately 50 cp. Reservoir depth of approximately 1,000 ft enables extremely rapid drilling. Oil-production revenue is more than 95% of total sales, and virtually all wells use sucker-rod pumps (SRPs). The key operational focus of these fields concerns the challenge of maintaining this very large number of wells at optimum production. An online system for well surveillance and well-services management was installed in the SJVBU, and the experience of implementing this system was used in the Cymric field. Cymric is typical of the SJVBU fields and contains approximately 800 SRP wells producing 16,000 BOPD. Cymric has another 500 huff ‘n’ puff cyclic-steam wells that flow after the steam cycle, adding another 24,000 BOPD, for a total field production of 40,000 BOPD. Automation History In the 1980s, a program to increase production in the Lost Hills field was based on finding the best method to fracture the wells. Field production rose from less than 3,000 BOPD to more than 20,000 BOPD. Managing this new production became a priority, and pump-off controllers (POCs) were installed throughout the field similar to that shown in Fig. 1.

Multimethod detrital thermochronology of the Great Valley Group near New Idria, California

The simultaneous use of several thermochronological methods on replicate sedimentary rock samples can reveal their pre- and postdepositional history. Single grain U/Pb dating of zircon, zircon and apatite fi ssion track dating, and vitrinite refl ectance measurements were performed on Cretaceous through Miocene sedimentary rocks of the Great Valley Group and the Temblor Formation near Coalinga and New Idria, California. The data show that the Sierra Nevada was exhumed and cooled at ~0.5–1 km/m.y. or ~20 °C/m.y. during the Cretaceous. After deposition in the Great Valley forearc basin, Sierra Nevada erosional products were buried at great depth under low thermal gradients. At ca. 12–14 Ma, northward progression of the Mendocino triple junction triggered folding on the eastern fl anks of the California Coast Ranges and rapid exhumation of the New Idria serpentinite diapir. This middle Miocene event caused the deposition of spectacular deposits of sedimentary serpentinite (Big Blue Formation). The rapid rise of the hot serpentinite body created a thermal pulse that may have provided the enigmatic heat source for oil fi elds in the shallow Vallecitos syncline, a few kilometers north of New Idria.

Completion Design and Implementation in Challenging HP/HT Wells in California

Summary As producing companies search for significant hydrocarbon resources, it has become necessary to pursue opportunities in frontier geologic horizons and geographic locations. This pursuit frequently results in encountering high-pressure/high-temperature (HP/HT) environments. The petroleum industry defines HP/HT wells as those exceeding 10,000 psi and 300°F. Several companies have drilled into HP/HT horizons in the California San Joaquin basin in the past 30 years, but operations were generally halted because of equipment limitations or limited hydrocarbon indications. In late 1998, a significant gas flow was identified from the Temblor formation at depths lower than 17,100 ft, with geologic information indicating a potential Temblor sand gross thickness of up to 3,600 ft. The pressure design basis for subsequent wells assumed an estimated equivalent pore pressure of 16.9 lbm/gal. This information and other producing conditions indicated a potential bottomhole environment of 425°F and 18,000 psi. Produced fluids also indicated the presence of hydrogen sulfide (H2S), which, at these pressures, dictates sour service metallurgical specifications. These potential, extreme well conditions require a very detailed completion engineering design, equipment qualification, rigorous planning, and precise field execution to achieve successful well completions. This paper details and discusses the well completion design basis and issues, equipment/perforating limitations and qualification tests, tubular stress and loading analyses, high-density completion-brine usage, and actual field operational experiences. Numerous contingencies were planned in detail, some of which had to be implemented. The most significant contingency operation was a high-pressure coiled-tubing milling operation to clean out 2,500 ft of formation and perforating debris that plugged the tubing string.

Local and regional tectonic control on sedimentology and stratigraphy in a strike-slip basin: Miocene Temblor Formation of the Coalinga area, California, USA

Sedimentological study of the Lower to Middle Miocene Temblor Formation in the Coalinga area of the San Joaquin basin (California, USA) provides new results applicable to understanding patterns of sedimentation and stratigraphic architecture in strike-slip basins along tectonically active margins. Detailed investigation of surface outcrops on the Coalinga anticline is integrated with description of cores from an adjacent oil field. This approach yields information on lateral variability of facies as well as vertical sequences, which contributes to deciphering the facies geometry and stratigraphic pattern. Five facies tracts are identified in the Temblor Formation (in ascending order): incised valley, estuarine, tide- to wave-dominated shoreline, diatomite, and subtidal. The vertical succession of facies tracts represents overall relative rise in sea level punctuated by episodes of non-deposition and exposure. Sediment accommodation was produced initially by incision of topography into the underlying Kreyenhagen Shale during relative sea-level fall and lowstand. Incised valley and estuarine facies tracts were deposited during subsequent rise in sea level. As additional accommodation was created by tectonic subsidence, tide- to wave-dominated, diatomite, and subtidal facies tracts were deposited. Periods of relative sea-level fall produced depositional hiatuses, some of which are overlain by distinctive shell-lag beds. The Temblor Formation represents deposition in an area influenced by along-strike tectonic variability associated with transform motion between the Pacific and North American plates. Stratigraphic study suggests that subsidence and uplift related to the transform boundary played a key role in deposition of the formation. Stratigraphic variations reflect the combination of basinal subsidence caused by regional extension and local uplift related to plate movement along the San Andreas transform zone. It is likely that strata deposited along other transform boundaries record similar tectonic effects.

２０世紀からの贈り物 掘削トラブルからの教訓 掘削深度の延長を可能にした新技術裸坑補強処理

Insufficient borehole pressure integrity (BHPI) is a major drilling challenge in deep, high-temperature, high-pressure (HTHP) wells in California and other areas. Shale and sandstone formations with low BHPI may be weakened by leaking faults/fractures or poor rock properties, causing lost returns with mud weights close to pore pressures. Drilling through depleted or low pore pressure formations with some probability of drilling into higher pressured zones in the same hole section compounds the severity of this challenge in the Temblor formation in Kern County, California.This challenge was solved by an innovative treatment applied in the Berkley East Lost Hills No. 1 well. Compared to conventional methods, it increased leakoff test (LOT) and formation integrity test (FIT) pressures to incremental values higher than those typically seen in the industry. Increasing BHPI allowed an additional 293m to be drilled before a 7-in, liner was set, and the well was drilled to 6, 012m. This depth met the objective of the well (to obtain full penetration through the objective sands) and allowed the subsequent discovery of a pay zone. If the new treatment to increase the LOT had not been used, the 7-in, liner would have been set early, and it is unlikely that the discovery zone would have been penetrated. Preventing skin and formation damage in potential zones of interest while treating weak points was another major concern heightened by a wide range of pore pressures. This paper discusses a theoretical mechanism to help explain how the treatment rapidly and substantially increases pressure integrity across both sand and shale formations. Minor penetrations in high and low permeability sandstone core tests help explain why the treatment system minimizes or prevents skin damage. Skin damage in the zones of interest may be prevented or minimized by BHPI treatments that only enter leaking fractures or faults. Further development and deployment of BHPI treatment technology promises a step change in industry practice to optimize well plans with lower cost programs for drilling fluids, casing design, cementing, and completion equipment. Optimized well designs should reduce both drilling days and flat time by allowing operators to drill smaller-diameter holes while using fewer casing strings to achieve the same production string dimensions.

Geologic study and multiple 3-D surveys give clues to complex reservoir architecture of giant Coalinga oil field, San Joaquin Valley, California

Coalinga is a giant oil field in the San Joaquin Valley of California (Figure 1) with an extremely complex subsurface stratigraphy, resulting in high operating costs relative to many other fields in the basin. Integration of stratigraphic interpretations based on core and outcrop with recently acquired 3-D seismic data and an extensive well log database enabled development of a sequence stratigraphic model encompassing the main producing reservoirs in West Coalinga Field. Our understanding of horizon maps and vertical reservoir connectivity has undergone significant changes, influencing development decisions for the field. Further integration of this new model with lithofacies descriptions, distributions, petrophysical, and production data are ongoing. Computer-based reservoir models for fluid-flow simulation and optimizing steam injection are being developed and hold additional promise for minimizing operating costs and maximizing production from this giant field. Figure 1. Proximity of Coalinga Field to the San Andreas Fault on the west side of the San Joaquin Valley. Lower to Middle Miocene strata are prolific hydrocarbon reservoirs in several San Joaquin Valley oil fields. On the west side of the valley, these rocks, called the Temblor Formation, have produced about 1.2 billion bo from several fields. Coalinga, by far the largest, has produced 850 million bo since 1887. Although recent development has significantly increased production from Pliocene sandstones of the Etchegoin Formation (Taschman, 1982), 90% of the current production is from nearshore to nonmarine, Middle Miocene sandstones of the Temblor Formation at depths of 500–4500 ft. Porosity averages 34% and permeability is 20–4000 millidarcies. Most reservoirs in the San Joaquin Valley are sourced by the Upper Miocene Monterey Formation. In contrast, Temblor Formation oil at Coalinga derives from organic-rich shales of the underlying Middle Eocene Kreyenhagen Formation (Peters et al., 1994; Clark et al., 2000). Although the field was discovered in 1887, significant production did not …