Offshore Sandstone Research Articles

Assessment of CO2 Sequestration Operation in an Offshore Sandstone Formation in the Pearl River Mouth Basin, South China Sea

Assessment of CO₂ Sequestration Operation in an Offshore Sandstone Formation in the Pearl River Mouth Basin, South China Sea

A novel reservoir classification method for sandstone reservoir evaluation using multi-scale digital rock method

The formulation of an effective development plan, optimizing exploitation efficiency, relies heavily on accurate reservoir characterization. However, existing reservoir classification methodologies, which rely on macroscopic geological observations and well-logging data, have limitations in data availability and fail to capture micro-scale pore structure characteristics accurately. The emerging technology of digital rock, widely employed in the petroleum industry, also faces challenges in accurately capturing reservoir heterogeneity due to its single-scale nature and limited application for reservoir classification. To overcome these challenges, this study presents an innovative reservoir classification approach based on the multi-scale digital rock method. This approach integrates qualitative assessment of micro-CT images for particle contact relationships and pore types with quantitative evaluation of multi-scale characteristic parameters, obtained from micro-CT and scanning electron microscopy (SEM) images. The proposed classification method demonstrates excellent agreement with the prioritization of development and production data for offshore sandstone reservoirs. By establishing a robust evaluation methodology, this classification method facilitates exploration potential assessment and development strategy optimization within the field.

Factor Analysis and Prediction on Recovery Efficiency in Offshore Sandstone Reservoirs with Thick–Thin Interbedding

Factor Analysis and Prediction on Recovery Efficiency in Offshore Sandstone Reservoirs with Thick–Thin Interbedding

Nitrogen Foam Alternating Flooding Experiment in The Offshore Strong Bottom Water Sandstone Reservoir

The CFD oilfield is located in the Bohai Sea area and is a typical offshore sandstone reservoir with strong bottom water. The characteristic of the rapid increase in water content is that it quickly enters a highly high water content period, and there currently needed to be more potential tapping measures affected by offshore production facilities. The development mode should be changed to explore the development effect of nitrogen foam flooding. This study conducted two experiments. The first experiment is a gas injection expansion experiment, which studied the changes in bubble point pressure, fluid volume, density, and viscosity under different gas injection conditions. The second experiment used a high-temperature and high-pressure oil displacement device and a long core for oil displacement experiments. Two typical sand bodies were selected for the N2 foam oil displacement experiment. The experimental results show that nitrogen injection has little effect on the properties of reservoir crude oil, with a viscosity reduction effect of 12.4% for heavy oil and 20.0% for thin oil. The viscosity of crude oil significantly impacts the selection of alternative media. The channel was prone to blockage and low oil displacement efficiency when injecting a single gas medium into a heavy oil system. The displacement efficiency of thin oil nitrogen foam is 73.28%. The displacement efficiency of nitrogen foam flooding for heavy oil is 43.09%. This study has a guiding significance for developing development plans for offshore sandstone reservoirs.

Exploring the Unique Characteristics of High-Pore-Volume Waterflooding and Enhanced Oil Recovery Mechanisms in Offshore Sandstone Reservoirs Using Nuclear Magnetic Resonance Technology

A single paragraph of about 200 words maximum. For research articles, abstracts should give a pertinent overview of the work. We strongly encourage authors to use the following style of structured abstracts, but without headings: (1) Background: Place the question addressed in a broad context and highlight the purpose of the study; (2) Methods: briefly describe the main methods or treatments applied; (3) Results: summarize the article’s main findings; (4) Conclusions: indicate the main conclusions or interpretations. The abstract should be an objective representation of the article and it must not contain results that are not presented and substantiated in the main text and should not exaggerate the main conclusions.

A robust age model for the Cryogenian Pocatello Formation of southeastern Idaho (northwestern USA) from tandem in situ and isotope dilution U-Pb dating of volcanic tuffs and epiclastic detrital zircons

Abstract Tandem in situ and isotope dilution U-Pb analysis of zircons from pyroclastic volcanic rocks and both glacial and non-glacial sedimentary strata of the Pocatello Formation (Idaho, northwestern USA) provides new age constraints on Cryogenian glaciation in the North American Cordillera. Two dacitic tuffs sampled within glacigenic strata of the lower diamictite interval of the Scout Mountain Member yield high-precision chemical abrasion isotope dilution U-Pb zircon eruption and depositional ages of 696.43 ± 0.21 and 695.17 ± 0.20 Ma. When supplemented by a new high-precision detrital zircon maximum depositional age of ≤670 Ma for shoreface and offshore sandstones unconformably overlying the lower diamictite, these data are consistent with correlation of the lower diamictite to the early Cryogenian (ca. 717–660 Ma) Sturtian glaciation. These 670–675 Ma zircons persist in beds above the upper diamictite and cap dolostone units, up to and including a purported “reworked fallout tuff,” which we instead conclude provides only a maximum depositional age of ≤673 Ma from epiclastic volcanic detritus. Rare detrital zircons as young as 658 Ma provide a maximum depositional age for the upper diamictite and overlying cap dolostone units. This new geochronological framework supports litho- and chemostratigraphic correlations of the lower and upper diamictite intervals of the Scout Mountain Member of the Pocatello Formation with the Sturtian (716–660 Ma) and Marinoan (≤650–635 Ma) low-latitude glaciations, respectively. The Pocatello Formation thus contains a more complete record of Cryogenian glaciations than previously postulated.

Sensitivity Analysis of Offshore Sandstone Reservoir—A Case Study of an Oilfield in the Western Bohai Sea

X oilfield is located in the Western Bohai Sea. During the water injection development process, the oil well productivity continued to decline. The effect of water injection and oil increase is poor. This time, by analyzing the sensitivity of the reservoir, the damage mode of the reservoir is analyzed, the reasons for the poor water injection effect are obtained, because of strong water sensitivity, medium to strong stress sensitivity, and the corresponding measures and suggestions are put forward, such as greater than 4500 mg/l of the salinity of injected water, timely supplement formation energy. Provide basis for the development of similar oil fields.

Displacement behavior and mechanism of long-term water flooding in sandstone oil reservoirs

Sandstone oil reservoirs with huge bottom water and high permeability are generally developed with high flow rate. After long-term water flooding (LTWF), the water flooding characteristics are quite different from that of original reservoir. In this paper, the effects of the PV number, viscosity, and displacement rate during LTWF are studied through experiments. The mechanism is analyzed based on analysis of changes in oil composition, rock mineral composition and wettability. The oil-water relative permeability curves, oil recovery and wettability were obtained with new experiments methods, which avoids the oil metering error by measuring oil and water separately. The research indicates that when the viscosity increases, the water phase permeability decreases, the residual oil saturation increases, and the water content rate increases earlier. A higher water flooding rate results in a higher ultimate recovery. A higher asphaltene content results in a higher viscosity and more oil-wet reservoir conditions. After LTWF, the wettability tends to water-wet, which is more favorable for heavy oil recovery. Moreover, LTWF reduces the clay content, which creates a more water-wet surface and a larger reservoir pore throat environment. This research provides insightful characteristics of offshore sandstone oil reservoirs, which can be used to enhance oil recovery.

Recovery Method and Parameter Optimization of a Pilot Test for Conformance Control Flooding and Thermal Recovery in the Offshore Heavy Oilfield

NB35-2 oilfield is a typical offshore sandstone reservoir with viscous crude oil and high permeability. Due to the inherent severe heterogeneity, the efficiency of conventional water flooding is pretty low and usually accompanied with early water breakthrough. In order to recover the residual oil and better realize its potential, applications of enhanced oil recovery (EOR) technology are necessary. However, the selection of EOR method and related parameters may directly impact the final results and can be noticeably different for different reservoirs; therefore, to optimize the oil production rate and final oil recovery, systematical optimization of every detail based on the condition of a specific reservoir is of key importance. In this paper, physical simulations were first conducted to select the best recovery methods for the target area based on the static geophysical model under the guidance of reservoir engineering theory. Then, detailed development variants for each method were determined by numerical simulation with the support of data obtained from previous pilot tests (polymer gel flooding and thermal fluid huff and puff) conducted in this area. Three exploitation methods were developed for the target well group, including polymer gel flooding (conformance control, Pattern 1), steam huff and puff (thermal recovery method, Pattern 2), and a combination of polymer gel flooding and steam huff and puff (conformance control and thermal recovery, Pattern 3). The numerical simulation result also showed that Pattern 3 yielded the highest oil recovery. Moreover, the amount of additional oil being recovered by applying Pattern 3 was even higher than the total additional oil being extracted by Patterns 1 and 2. In addition, sensitivity analysis was conducted to rank the most important parameters based on the three Patterns. At last, it is thought that the synergistic effect between conformance control and thermal recovery made more oil recovered, which was intuitively clarified in the mechanism analysis.

Screening of Enhanced Oil Recovery Methods in One of Iran’s Offshore Oil Fields

Enhanced oil recovery (EOR) is a vital part of the process of oil production from sandstone and carbonate reservoirs. Maintaining and increasing oil production from many fields require proper selection, design, and implementation of EOR methods. The selection of EOR methods for specific reservoir conditions is one of the most difficult tasks for oil and gas companies. Screening of different EOR techniques considering previous experiences from the methods applied in other fields is a first step in the recommendation of any costly EOR operations. In this paper, EORgui software was utilized to screen eight enhanced oil recovery methods in one of Iran’s offshore sandstone oil fields. The reservoir is composed of two sections with different fluid properties, namely API, viscosity, and oil composition, but relatively homogeneous rock properties and high permeability (1500 mD). The results show that polymer flooding is technically the most suitable enhanced oil recovery method in the upper zone of the reservoir with a high percentage matching score of 90%, and immiscible gas injection with a matching score of 83% is ranked second. For the lower part of the reservoir containing a fluid with much higher viscosity, immiscible gas injection (83% matching) can be recommended. Furthermore, polymer flooding predictive module (PFPM) was utilized to investigate the impact of polymer concentration on oil recovery performance of the upper part with an ultimate recovery of about 40% at the optimum concentration.

Reconnaissance composition of river sand from northern South Island, New Zealand: a modern analogue for southern Taranaki Basin

ABSTRACTThe composition of 20 modern sand samples (18 streams, one beach, and one lakeshore) collected from the northern South Island provide a dataset for assessing detrital signatures of Paleozoic-Mesozoic basement terranes that may have served as sediment sources for reservoir sandstones in the Taranaki Basin. Non-plutonic terranes produce lithic-rich sand dominated by metamorphic fragments. Samples derived from erosion of the Rakaia and Caples terranes are more quartz-rich than the other non-plutonic terrane samples. Sand from the Dun Mountain-Maitai and Brook Street terranes has the lowest quartz content and is further distinguished by detrital serpentine. Pervasive pumpellyite-bearing metamorphic lithic fragments characterise the Caples, Dun Mountain-Maitai and Brook Street terranes. Feldspar is rare in Eastern province terrane sand. Sand from the Median Batholith tends to have less quartz than sand from the Karamea Batholith and a higher percentage of plagioclase, while sand from the Karamea Batholith has a higher proportion of potassium feldspar. Petrographic analyses were compared with published reports describing the composition of offshore sandstone reservoirs to evaluate their likely provenance.

The Offshore Bar Revisited: A New Depositional Model For Isolated Shallow Marine Sandstones In the Cretaceous Frontier Formation of the Northern Uinta Basin, Utah, U.S.A.

Abstract Shallow marine sandstone bodies isolated within marine mudrock successions are still incompletely understood. A robust understanding of such bodies is of interest not only scientifically, but also in order to facilitate successful exploration for and production of petroleum and other natural resources. Such bodies are preserved in the Turonian Frontier Formation of the northern Uinta Basin in Utah and Colorado, U.S.A., where they have been previously interpreted as the products of “offshore bars.” A reappraisal of these bodies in the uppermost Frontier Formation (herein defined as the Turonian Ashley Valley Member) reveals three northeast–southwest elongate, incised highstand, forced regressive, and lowstand offshore sandstone bodies partially to fully encased in offshore marine mudrock. These bodies are herein named the Buckskin Hills, Kane Hollow, and Raven Ridge sandstones (from oldest to youngest). Five lithofacies were identified from 47 measured outcrop sections located along the western and southern margins of Dinosaur National Monument. They are 1) marine shelf claystones and siltstones, 2) lower–upper offshore marine admixed siltstone and sandstone, 3) lower–upper offshore thin-bedded sandstones and siltstones, 4) distal lower shoreface heavily bioturbated very fine-grained sandstone, and 5) transgressive lag conglomerate. Wireline logs from 112 drillhole locations throughout the Uinta Basin were calibrated with nearby outcrop locations to construct cross sections and net-sandstone isochore maps. From these, regionally traceable horizons (flooding surfaces and internal erosion surfaces) facilitated an analysis of stacking patterns, development of a stratigraphic framework, and a depositional-environment interpretation. Overall, the Ashley Valley Member preserves a basinward-offlapping stacking pattern, indicative of shoreline progradation in response to the late Turonian Greenhorn global eustatic regression that was interrupted by two, high-frequency transgression–regression cycles. This nested cyclicity cannot be explained by global eustasy alone, and instead is suggestive of a secondary allogenic control, likely related to Western Cordilleran Foreland Basin (WCFB) geodynamic driving mechanisms. As a result, the Ashley Valley Member provides an example of tectonic forcing on stratal stacking patterns, highlighting the importance of intrabasinal tectonic processes on dispersal patterns and high-frequency relative base-level fluctuations within the WCFB stratigraphic record.

Field Treatment To Stimulate an Oil Well in an Offshore Sandstone Reservoir Using a Novel, Low-Corrosive, Environmentally Friendly Fluid

Summary Acidizing sandstone formations is a real challenge for the oil and gas industry. Fines migration, sand production, and additional damages caused by precipitation are some of the common concerns related to sandstone treatments. Furthermore, the complexities of sandstone formations require a mixture of acids and loadings of several additives. The environmentally friendly chelating agent glutamic acid N,N-diacetic acid (GLDA) was used successfully to stimulate deep gas wells in carbonate reservoirs. It was tested extensively in the laboratory to stimulate sandstone cores with various mineralogies. Significant permeability improvements were reported in previous papers over a wide range of conditions. In this paper, the result of the first field application is evaluated with a fluid based on this chelating agent to acidize an offshore, sour oil well in a sandstone reservoir. The field treatment included pumping a preflush of xylene to remove oil residues and any possible asphaltene deposited in the wellbore region, followed by the main stage that contained 25 wt% GLDA, a corrosion inhibitor, and a water-wetting surfactant. The treatment fluids were displaced into the formation by pumping diesel. The treatment fluids were allowed to soak for 6 hours, then the well was put into production, and samples of flowback fluids were collected. The concentrations of key cations were determined using inductively coupled plasma, and the chelant concentration was measured using a titration method with ferric chloride solutions. Corrosion tests conducted on low-carbon-steel tubulars indicated that this chelant has low corrosion rates under bottomhole conditions. No corrosion-inhibitor intensifier was needed. The treatment was applied in the field without encountering any operational problems. A significant gain in oil production was achieved without causing sand production, or fines migration. Analysis of flowback samples confirmed the ability of the chelating-agent solution to dissolve various types of carbonates, oxides, and sulphides, while keeping the dissolved species in solution without causing unwanted precipitation. Unlike previous treatments conducted on this well, where 15 wt% hydrochloric acid (HCl) or 13.5 wt%/1.5 wt% HCl/hydrofluoric acid (HF) acids were used, the concentrations of iron and manganese in the flowback samples were negligible, confirming the low corrosion rates of well tubulars when using GLDA solutions.

Benthic foraminifera from the Lower Jurassic transgressive mudstones of the south-western Barents Sea—a possible high-latitude expression of the global Pliensbachian–Toarcian turnover?

The Lower Jurassic section of two commercial wells (7119/12-1 and 7119/12-2), drilled in the Hammerfest Basin, was analysed for foraminiferal assemblages in order to reconstruct palaeoenvironmental changes. Foraminifera occurred singularly in transgressive mudstone intervals of the Stø Formation in well 7119/12-1. High-energy marginal marine and offshore sandstones and freshwater sand- and mudstones were barren of foraminifera. Three distinct foraminiferal assemblages could be distinguished. They contain exclusively agglutinated taxa and have extremely low species diversities, indicating restricted environmental conditions. The main restricting factor was low salinity in strongly delta-influenced waters. Foraminiferal assemblage 1 is developed at the base of the Stø Formation and suggests transgressive, extremely hyposaline lagoonal conditions. Assemblages 2 and 3 occur in hyposaline prodelta shelf mudstones of the Stø Formation and reveal increased diversities in major local transgressive phases. The foraminiferal assemblages indicate Pliensbachian–Toarcian ages. The mudstones of the Stø Formation are regarded as a local expression of the global Pliensbachian–Toarcian turnover recording regional transgressive developments in the Toarcian.Keywords: Barents Sea; foraminifera; marginal marine environments; Early Jurassic; Pliensbachian–Toarcian turnover.(Published: 28 January 2014)Citation: Polar Research 2014, 33, 20206, http://dx.doi.org/10.3402/polar.v33.20206

Sharp‐based marine sandstone bodies in the Mulichinco Formation (Lower Cretaceous), Neuquén Basin, Argentina: remnants of transgressive offshore sand ridges

AbstractThe interpretation of sharp‐based shallow‐marine sandstone bodies encased in offshore mudstones, particularly transgressive units, has been a subject of recent debate. This contribution provides a multiple‐dataset approach and new identification criteria which could help in the recognition of transgressive offshore sandstone bodies worldwide. This study integrates sedimentology, ichnology, taphonomy and palaeoecology of Mulichinco Formation strata in the central Neuquén Basin (Argentina) in order to describe and interpret sharp‐based sandstone bodies developed in ramp‐type marine settings. These bodies are sandwiched between finer‐grained siliciclastics beneath and thin carbonates above. The underlying sediments comprise progradational successions from offshore mudstones to offshore transition muddy sandstones, grading occasionally into lower shoreface sandstones. The surfaces capping the regressive siliciclastics are flat and regionally extensive, and are demarcated by skeletal concentrations and a Glossifungites suite; they are also marked by sandstone rip‐up clasts, with encrustations and borings on all sides. These surfaces are interpreted as composite discontinuities, cut during a relative sea‐level fall and remodelled during the initial transgression. The overlying transgressive sandstone bodies are 3 to 7 m thick, >4 km long and about three times longer than wide; they are composed of fine‐grained sandstones with little lateral change in grain size. Cross‐stratification and/or cross‐lamination are common, typically with smaller‐scale structures and finer grain size towards the top. Large‐scale, low‐angle (5° to 8°) inclined stratification is also common, dipping at ca 30° with respect to body elongation and dominant currents. These sandstone bodies are interpreted as offshore sand ridges, probably developed under the influence of tidal currents. Intense burrowing is typical at the top of each unit, suggesting an abandonment stage. Final deactivation favoured colonization by epibenthic‐dominated communities and the formation of skeletal‐rich limestones during the latest transgressive conditions. As partial reworking of pre‐existing ridges occurred during this stage, the Mulichinco sandstone bodies are considered the remnants of transgressive offshore sand units.

Evaluation and prevention of formation damage in offshore sandstone reservoirs in China

Reduction in water injectivity would be harmful to the waterflood development of offshore sandstone oil reservoirs. In this paper the magnitude of formation damage during water injection was evaluated by analyzing the performance of water injection in the Bohai offshore oilfield, China. Two parameters, permeability reduction and rate of wellhead pressure rise, were proposed to evaluate the formation damage around injection wells. The pressure performance curve could be divided into three stages with different characteristics. Analysis of field data shows that formation damage caused by water injection was severe in some wells in the Bohai offshore oilfield, China. In the laboratory, the content of clay minerals in reservoir rock was analyzed and sensitivity tests (including sensitivity to water, flow rate, alkali, salt and acid) were also conducted. Experimental results show that the reservoir had a strong to medium sensitivity to water (i.e. clay swelling) and a strong to medium sensitivity to flow rate, which may cause formation damage. For formation damage prevention, three injection schemes of clay stabilizer (CS) were studied, i.e. continuous injection of low concentration CS (CI), slug injection of high concentration CS (SI), and slug injection of high concentration CS followed by continuous injection of low concentration CS (SI-CI). Core flooding experiments show that SI-CI is an effective scheme to prevent formation damage and is recommended for the sandstone oil reservoirs in the Bohai offshore oilfield during water injection.

Sedimentologic and tectonic origin of an incised-valley-fill sequence along an extensional marginal-lacustrine system in the Basin and Range province, United States: Implications for predictive models of the location of incised valleys

Incised valleys in extensional lacustrine systems should be common and significant petroleum targets, yet documentation and analysis of these systems are limited and, hence, so are predictive models for their location. Geologic mapping of the Miocene–Pliocene Humboldt Formation in Knoll basin, northeastern Nevada, has revealed a significant incised-valley system formed along the lacustrine margins of an extensional basin. The valley formed during a relative lake-level fall and incised into lacustrine shoreface and offshore sandstone and subsequently was filled with fluvial and eolian sediment as lake level rose. The valley's location was tectonically influenced; it is situated in the hinge zone of a syncline near the tip of the range-bounding fault system. Folding of the syncline was broadly synchronous with incision and filling, and it appears to have localized the valley along the topographically low hinge zone. Furthermore, the large relative lake-level change that produced the valley is only recorded in strata in the syncline area, suggesting that the location and cause of incision was greatly influenced by tectonics. Thus, the location of similar incised valleys in other extensional basins may be predictable if comparable tectonic features and processes are recognized. Our study suggests that the best locations to develop and preserve incised valleys are near the tips of normal faults during periods of overall high tectonic subsidence. Specific areas along basin-bounding faults where tectonically influenced incised valleys are more likely to form include fault-propagation folds, synthetic relay ramps near transfer faults, and areas that have large changes in fault slip. Although lake volume changes caused predominantly by climate change can be an important factor in producing incised valleys, tectonically influenced incised valleys are likely to be larger, better preserved, and more petroleum prone compared to climate-controlled incised valleys.

Depositional environment and taphonomy of the ‘strings of beads’: Mesoproterozoic multicellular fossils in the Bangemall Supergroup, Western Australia

Enigmatic Mesoproterozoic bedding‐plane structures, informally known as ‘strings of beads’, are common in the Bangemall Supergroup in Western Australia and the Belt Supergroup in North America. The Belt Supergroup structures are formally known as Horodyskia moniliformis, and age constraints show that they are more than 350 million years older than similar 1070 Ma structures in the Bangemall Supergroup. Strings of beads in the Bangemall Supergroup have previously been interpreted as fossils of multicellular organisms based on their morphology and on statistical comparisons with a range of organic and inorganic structures. However, details of their depositional environment and taphonomy, which can provide important insights into their origin, are poorly known. This study shows that strings of beads in the Backdoor Formation of the Bangemall Supergroup were deposited in a subtidal marine‐shelf environment in association with microbial mats and enigmatic dimple marks. The structures are preserved at the base of fine sandstone beds within shoaling‐upward shelfal mudstone and sandstone packages deposited below storm wave‐base. Following deposition from suspension, the strings of beads were bound to the sea floor by microbial mats and their associated mucilage, preventing realignment by palaeocurrents. Relationships between the strings of beads and dimple marks in offshore sandstones suggest that the latter may represent holdfasts to which the strings were originally attached.

A storm-dominated offshore sandstone interval from the Corallian Group (Upper Jurassic), Weald Basin, southern England

The Upper Jurassic Corallian Group of the subsurface of the Weald Basin, southern England, contains two stacked marine sand bodies. They have an elongate geometry (9–25 m thick, 100 km long, 30 km wide) and consist predominantly of cross-bedded, fine to medium grained, glauconitic sandstones with bioturbated, low angle cross-laminated silty sandstones. The sandbodies trend east-west, subparallel to the palaeoshoreline, but oblique with respect to the south-easterly palaeocurrent direction. In general, facies are stacked in progressively upward-coarsening sequences with lower clays passing up into bioturbated siltstones, followed by various types of cross-bedded, medium grained sandstones. The characteristics and distribution of the lithofacies indicate that these sandbodies are not shoreline deposits. However, they are strikingly like offshore sand ridges widely documented from the Cretaceous Western Interior seaway of North America. The lack of any typical features of tidal sandbodies and the common occurrence of erosively based, low angle cross-lamination resembling hummocky cross-stratification in the lower part of the coarsening upwards sequences indicate that storm currents may have been important in generating the Corallian offshore sandbodies.

Influence of Depositional Processes on the Composition of Sandstone in a Wave-Dominated Fan Delta: ABSTRACT

Sandstone in the Lower Pennsylvanian (Morrowan-Atokan) portion of the Fountain Formation in the Manitou Springs, Colorado, area was derived from Precambrian granite gneiss and deposited in associated medial alluvial-fan, foreshore, shoreface, and offshore environments constituting a wave-dominated fan delta. The sandstone facies are arranged in six vertically stacked progradational sequences. The regressive marine portions of the sequences rest on a transgressive lag conglomerate and range from 5 to 9 m thick. The alluvial deposits capping each sequence are up to 20 m thick. The different sandstone facies of the fan delta system show variations in mineralogical composition. Because all of the sandstone facies share a common first-cycle provenance and burial history, differences in composition largely reflect differences in depositional-process control on composition. Foreshore sandstones possess maximum compositional maturity; offshore sandstone is most immature. Apparently feldspar is winnowed out of the foreshore sand, bypasses the shoreface, and is concentrated in offshore, storm-deposited sand. Alluvial and shoreface sandstone are intermediate in composition with QFR content of 55:35:10 and 60:35:5, respectively.