Primary Fracturing Research Articles

Numerical simulation of hydraulic fracture propagation from recompletion in refracturing with dynamic stress modeling

Owing to the rapid decline of oil production from tight oil reservoirs after primary hydraulic fracturing treatment on the horizontal well, a refracturing stimulation is proposed for tight oil recovery. In this study, a fully coupled dynamic stress computational method with a finite-element method is presented, and depletion-induced dynamic stress is simulated by coupled numerical modeling. In addition, the extended finite-element method (XFEM) approach is used to investigate the effect of different parameters on fracture dynamic propagation in recompletion from refracturing. The results highlight the effects of production-induced stress changes following hydraulic fracture propagation. When multiple fractures are stimulated simultaneously from recompletion during refracturing, curved fractures are commonly observed, and the deflected fractures generally divert toward the primary stimulated area with low pore pressure. The results indicate that comprehensive factors can affect the hydraulic fractures propagation from recompletion. The optimal refracturing time window can be determined using the dynamic stress condition and stimulated area. The initial completion spacing, initial fracture length, and recompletion perforation cluster spacing can also affect the fracture geometry from the recompletion. A larger initial fracture length can induce a larger stress change area, whereas a larger distance between the new perforations in recompletion and the old perforations can decrease the depletion-induced stress effect. A high horizontal stress contrast can increase the depletion-induced stress effect because a long fracture extends the area. Owing to the nonuniform pressure and stress distributions, more nonuniform fractures are commonly generated in the refracturing treatment. Thus, temporary plugging injection and proppant inertia must be designed while reducing the number of perforations near the initial perforation positions. This can help decrease the possibility of strong curved fractures and screen out problems.

METHOD FOR FORECASTING INCREASE IN LIQUID PRODUCTION FOR OPTIMIZE SELECTION OF CANDIDATES FOR HYDRAULIC FRACTURING

Over the past 20 years, the structure of reserves of Russian oil fields has undergone significant changes: with a general increase in reserves, there has been a significant increase in the share of hard to recover reserves (HTR). In the HTR structure of the Russian Federation, low-permeability and heterogeneous reservoirs are identified as the main subgroup (64 %), in 2022, approximately 30 % of all Russian oil was produced from HTR (166 from 535 million tons). In such reservoirs, to maintain and ensure high levels of oil recovery, a workovers such as hydraulic fracturing (HF) is used.Petroleum production companies have various technical and infrastructal capabilities for the selection of candidate wells for workover. Some oil companies use the support of design institutes and service companies that mining andhave specialized geological software products for monitoring and selection of workovers, others make do with the knowledge and skills of selecting their own specialists. However, due to the development of residual recoverable reserves and the unprofitability of the workover every year to select candidate wells, it is becoming increasingly difficult to select candidate wells. Working out the entire well stock and selection candidate wells using standard techniques takes a huge amount of time for a specialist. The article proposes a solution to the topical issue of optimizing the selection of candidate wells for hydraulic fracturing by predicting the dynamics of production wells based on historical data for various geological conditions. The developed method for forecasting the flow rate of liquid and oil on the basis of the rate of change in reservoir pressure and water cut of the well allows you to predict the flow rate for two years ahead, monthly estimates the possible increase from hydraulic fracturing and allows you to determine the optimal time for repeated or primary hydraulic fracturing at the well. This approach sharply narrows the number of potential candidates from a coupe of hundred to two to three dozen potential candidates.

Contextual relationship between mechanical heterogeneity and dyking: constraints from magma emplacement dynamics of the ca. 2.21 Ga Anantapur–Kunigal mafic dyke swarm, Dharwar Craton, India

AbstractMafic dykes are typically emplaced through primary hydraulic fracturing of undeformed crust or may make use of pre-existing crustal inhomogeneities, representing the plumbing systems of a large igneous province. The Eastern Dharwar Craton has dense exposures of several generations of Paleoproterozoic mafic dyke swarms ranging from ca. 2.37 Ga to ca. 1.79 Ga. Herein, using anisotropy of magnetic susceptibility fabric data of mafic dykes and associated host granites, the emplacement systematics of the NW- to W-trending ca. 2.21 Ga Anantapur–Kunigal dyke swarm, displaying a radiating geometry, have been studied to understand magma flow dynamics. A low-angle relationship between the silicate and opaque fabrics and good correlation with magnetic lineation, identified via petrographic studies and shape preferred orientation analyses of multiple oriented thin sections, suggest a primary flow-related magnetic anisotropy for the studied dyke samples. The classic subparallel relationship between the trend of the dyke planes and magnetic fabric of the associated host granites suggests that the radiating geometry of the ca. 2.21 Ga dyke swarm was supported by a favourable pre-existing structural grain of the country rock. We interpret the magma for the studied dyke swarm was fed laterally from a distant plume. It was emplaced as laterally propagating primary dyke fractures as well as injected into the pre-existing subparallel crustal inhomogeneities. Corroborating all these inferences, a detailed emplacement model for ca. 2.21 Ga Anantapur–Kunigal dyke swarm is also proposed.

Simulation of fracture propagation law in fractured shale gas reservoirs under temporary plugging and diversion fracturing

Natural fractures (NFs) are developed in shale gas reservoirs, which can easily cause frac hits during hydraulic fracturing and reduce the productivity of infill wells and parent wells. Temporary plugging diverting fracturing (TPDF) can hinder the single forward extension of fracture transition and avoid the communication of hydraulic fractures (HFs) or NFs adjacent to wells. In order to explore the fracture propagation law of TPDF in fractured shale gas reservoirs, this study systematically evaluates the main factors such as stress difference, displacement, and fracturing fluid viscosity on the fracture temporary plugging diversion (TPD) law by means of true triaxial hydraulic fracturing simulation device and cohesive element model in ABAQUS. The findings reveal that (1) the law of fracture initiation and propagation at the engineering scale is similar to that in indoor experiments. Upon the primary fracturing (PF), the smaller the horizontal stress difference, the larger the pumping displacement, and the smaller the viscosity of the fracturing fluid is, the greater the corresponding fracture breakdown pressure and the stronger the rock compression resistance. (2) After TPD secondary fracturing, a small horizontal stress difference and a large pumping displacement facilitate the formation of a vertical complex fracture network structure on the primary fracture. Because of the small size of the indoor rock, viscosity has little effect on the fracture propagation of the TPDF, but the numerical simulation results reveal that the higher the viscosity, the greater the width of the new fracture. In addition, (3) the smaller the angle between the new fracture opened after PF and TPDF, the better the propagation effect of the new fracture. Meanwhile, the farther the temporary plugging zone is from the fracture front end, the wider the new fracture opened after TPDF. The field construction results reveal that the TPDF technology can avoid the effect of HFs, thus preventing frac hits during shale gas reservoir reconstruction. This study not only posits a physical and numerical simulation method for simulating the fracture propagation law of TPDF in fractured shale gas reservoirs but also provides theoretical guidance for applying TPDF to field construction.

Optimization of the Water-Energy Nexus in Hydraulic Fracturing Processes Using CO2 and Water as Fracturing Fluids

Hydraulic fracturing has paved the way for the extraction of substantial quantities of shale gas. Traditionally, water (in significant quantities) has been used as the primary fracturing fluid. In addition to the significant water usage in fracturing, large quantities of shale gas wastewater have been generated. Driven by the need for better management of water resources in hydraulic fracturing, the introduction of CO2 (captured from industrial emissions) has been considered an element in the fracturing fluid. This paper proposes a mathematical programming formulation to synthesize the best configuration for the use of water and CO2 associated with shale gas hydraulic fracturing operations while taking into account the fluctuations in water availability, generation of CO2, and the flowback water based on a time horizon. The proposed formulation incorporates a strategic planning that minimizes the total annual cost (TAC) considering water requirements, generation and capture of CO2, as well as the capacity of the equipment for treatment technologies, transportation fees, storage units, and disposal. A case study is presented to demonstrate the usefulness of the proposed methodology. The results show that at a higher percentage of CO2 in the fracturing fluid, the TAC increases but the freshwater required decreases. Furthermore, the trade-offs and impact of freshwater availability have been identified.

Experimental research on hydraulic fracture propagation in group of thin coal seams

The commingled production technology has been applied in group of thin coal seams exploitation. In order to explore the mechanism of fracture extension of multi-layer combined fracturing in thin coal seam groups with different perforating location, fracturing fluid displacement and fracturing fluid viscosity, this paper firstly adopted sand/coal (single and two-layer) indoor experiment to explore the basic law of fracture propagation and effective fracturing methods in cataclastic coal. After that, the multilayers experiment was carried out, and the fracture propagation law was studied by two types of (Model A: 3 layers sandstone and 2 layers coal) and (Model B: 3 layers coal and 2 layers sandstone). The experimental study of coal/sandstone (single and two-layer model) showed that the fracture morphology of primary structure coal was relatively simple. When the fracturing fluid was injected into the cataclastic coal, it was difficult to form effective fractures and the scale of the fracture was small. Therefore, the perforating location in the cataclastic coal should be avoided. In the secondary fracturing of the cataclastic coal seam, the fiber fracturing fluid could seal the fracture system of the primary fracturing of cataclastic coal, which provided technical reference for secondary temporary plugging fracturing. In addition, the law of fracture propagation in multi-layer coal measure strata was studied on the basis of the single and two-layer model, and the fracture propagation was evaluated from the aspects of fracture propagation morphology, fracture scale and fracture penetration. Multi-layers experiments showed that whether hydraulic fracture could achieve the penetration effect was mainly affected by the perforating location. If the perforating location was in the sandstone layer, the facture was easy to penetrate coal seam. When the fracture penetrated the interface between two layers, the generated pressure pulse activated the weak surface of developed fractures in coal seam, prompting the formation of complex fracture. In addition, the larger the fracturing fluid displacement and the lower fracturing fluid viscosity, the easier it was for hydraulic fractures to form branch fractures or activate natural fractures, increasing the fracture propagation volume to maximize hydraulic fracture complexity in the formation. In this experiment, the fracture propagation law of hydraulic fracturing in thin coal seam groups was studied under different engineering factors from multiple perspectives. The research results could provide reference for the fracturing construction design in thin coal seam groups.

Research on Refracturing Technology of Horizontal Wells Based on Dynamic Drainage Volume

Refracturing is an important method to improve the productivity of low-yield and low-efficiency horizontal wells. Due to the influence of geological factors and primary fracturing, it is of great importance to select suitable candidate wells and determine reasonable refracturing timing. Considering that production and pressure are the first-hand data available in the fields, they can be used to evaluate the dynamic drainage volume of fractured horizontal wells and to predict refracturing timing combined with fracturing parameters. In this study, the stimulation potential of refracturing is evaluated by introducing the dynamic drainage volume, and the refracturing timing discrimination model is established. Based on this model, the refracturing timing charts of different initial fracturing scales are drawn. In addition, the reservoir numerical simulation method is used to optimize the method of horizontal well refracturing. The results show that it is advisable to repeat fracturing when the change rate of dynamic drainage volume growth rate is less than 10%. The refracturing methods of restoring the conductivity of fractures or sealing the original fractures and refracturing the new fractures have good development effects. The research is of great significance to the design of horizontal well refracturing.

Optimization of Re-Fracturing Method and Fracture Parameters for Horizontal Well in Mahu Conglomerate Oil Reservoir

Mahu Oilfield, the largest conglomerate oilfield around the world, is facing the severe problems of rapid production decline and low recovery ratio. Re-fracturing of horizontal wells is an effective method to improve this situation. The study of horizontal well re-fracturing has increased popularity recently, but the optimization of re-fracturing parameters has not been thoroughly investigated, especially for the conglomerate reservoir. The optimal selection of re-fracturing parameters such as length and conductivity is unclear, which significantly influences re-fracturing treatment and economic cost. In order to fill this gap, a series of numerical models are established based on filed data to predict horizontal well production after re-fracturing. The parameters of primary hydraulic fractures are calculated by net pressure matching and are imported into the numerical models. A production matching is conducted to confirm the reliability of numerical models. The cumulative productions of different re-fracturing stimulation methods, including lengthening old fractures and perforating new fractures, are simulated, and the corresponding re-fracturing parameters are optimized. The results have shown that the length of primary fractures is smaller than designed, which means lengthening old fractures is necessary. Lengthening old fractures and perforating new fractures between primary clusters can increase production. On the condition of the same fracture length, the increasing ranges of production corresponding to perforating new fractures are larger than that of lengthening old fractures. Lengthening old fractures is particularly suitable to the situation that the length of primary fractures is smaller than designed, and the optimal value in lengthening half-length of old fractures is 160 m. By contrast, perforating new fractures between old clusters applies to the case that the cluster spacing of primary hydraulic fracturing is larger than 35 m, and the optimal fracture half-length is 140 m.

Re-Fracturing Wells Selection by Fuzzy Comprehensive Evaluation Based on Analytic Hierarchy Process—Taking Mahu Oilfield as An Example

Re-fracturing treatments of horizontal wells are increasingly gaining popularity to address the issue of rapid production decline and low recovery ratio for the conglomerate reservoir of the Mahu Oilfield. How to effectively select the horizontal wells with potentiality for re-fracturing and conduct the re-fracturing operation to achieve the purpose is the key problem that needs to be investigated urgently. However, the conventional methods for vertical wells are not in our consideration, and some methods for horizontal wells have their limits for the Mahu reservoir. To cope with problems mentioned above, fourteen factors from geology parameters, engineering parameters, and production performance parameters are considered to establish a multi-level evaluation model to quantify the potentiality of each horizontal well for re-fracturing in the Mahu Oilfield. First, the analytic hierarchy process (AHP) is used to obtain the weights of various factors affecting the productivity of horizontal wells, and on this basis, the subordination degree and evaluation matrix are then calculated, and finally, the fuzzy synthetic determination is obtained to determine the candidate wells for re-fracturing. The results have shown that the weights corresponding to engineering parameters obtained by the AHP method are the largest, followed by geology parameters, and the weights of production performance parameters are the minimal relatively; the number of fractures and the sand quantity of single cluster are the main controlling factors in engineering factors, and the initial formation pressure is the main controlling factor in geological factors; there is obvious correlation between the cumulative oil production after 90 days of primary fracturing with final cumulative production. Wells M15, M13, and M7 rank top three among the candidate wells. Through re-fracturing treatment by temporary plugging, the daily oil production of well M15 has increased significantly and is even higher than that of the primary hydraulic fracturing stimulation, confirming the reliability of the proposed selection method.

Experimental study on mechanical properties of coal rocks in re-fracturing

Taking high rank coal in Qinshui Basin as the research object, the mechanical parameters of the coal rocks after primary fracturing with quartz sand filling the fracture are measured, and the variation law of the mechanical properties of the coal rocks after sand filling is analyzed to provide reliable technological parameters for multiple fracturing. The results show that Poisson's ratio is 22.6% higher than the initial average, Young's modulus is 47% lower than the initial average, and permeability of low-permeability coal seam is nearly 10 times higher. The results indicates that in the development of high rank coalbed methane, the change of mechanical properties caused by quartz sand filling after the first fracturing of coal rocks can provide relatively real basic data for the design of the second fracturing process and improve the reliability of the design.

Epithermal clast coating inside the rock avalanche-debris flow deposits from Mount Meager Volcanic Complex, British Columbia (Canada)

The observational and semi-quantitative sedimentological analyses of the lithofacies assemblage contribute to describe at different scales the breccia matrix along the sheared and transformed contact between rock avalanche deposits and trailing debris flow deposits emplaced by a large landslide at Mt. Meager volcano in British Columbia in 2010. An inverted cataclastic gradient of crushed breccias in a fluidized and mixed matrix implies a structurally controlled flow regime and rapid deposition. The coating matrix changed the initial polymodal distribution of the debris-flow lithofacies. Clast shape evolution helps to characterize the cataclastic sorting during transport and fluidized disaggregation. A plot of matrix percent against matrix/gravels helps to distinguish primary hot fracturing of about 61% from initial dilation and sheared fracturing involving ~22% matrix. Extensional disaggregation between 73 and 79% matrix is related to hydromagmatic fragmentation within an epithermal system. Clayey mineral assemblages identified by XRD patterns are related to colloidal aluminium gel, cataclastic shear bands, and quartz microstructures in epithermal breccia zones (pH = 2–3, 200–350 °C, <10–20 GPa).Microstructural analysis differentiates the inner rim of coated clasts from their border and the surrounding matrix in impact melt breccias. Sequential coating stages are inferred during the propagation of the shock wave with an oscillatory relative speed during the inter-seismic period. We differentiate: 1) shock faulting which contributes to the impacted quartz (10–35 GPa) in a devitrified matrix and pseudotachylite coating related to frictional melting at the margin of a conduit; 2) shock response (85 GPa) in epithermal vein with calcic spheroids, CO2 dissociation, and basaltic melt (70–101 GPa, >1500 °C); and 3) the secondary fracturing with flash heating and pressure pulse during cavitation (ΔP ~ 10 GPa, >1000–1500 °C), which generates pockets of partial melting, quartz spheroids, and a roll-over effect for the inner rim of coated clasts. The formation of impact melt breccias and the debris flow are related to the slowing elastic impact wave with an oscillatory relative speed during the inter-seismic period along a proximal strike-slip fault.This study helps identify how the proximal rock avalanche transformed into a highly mobile debris flow, larger examples of which pose a hazard to the town of Pemberton, at a distance of 65 km from Mt. Meager.

Response of pores in coal to repeated strong impulse waves

Repeated-strong-impulse-wave (RSIW) is a new development technique to enhance coalbed methane recovery. The objective of this paper is to investigate the response of pores to impacts using this device. Bituminous coals and anthracites were impacted, and their pores were analysed by mercury porosimetry, a scanning electron microscope and an optical microscope. The results show that pores of anthracite have limited sensitivity to impacts, and their evolution trend is inconspicuous with increasing the number of impacts. Pores of bituminous coal are remarkably sensitive to impacts. The pore evolution of bituminous coal presents two stages during impacts, sharply increasing and then decreasing slowly. Impacts at higher energy levels shorten the process of pore evolution. The distribution of pores seems to be a reason that smaller pores in size are more sensitive to impacts than the larger ones. The mechanical property results in the differences in responses to impacts between bituminous coal and anthracite. Therefore, it is determined that pre-existing crack propagation is the primary fracturing mode of anthracite. Pore initiation and propagation contribute markedly to the fracture of bituminous coal during impacts. However, their contribution is gradually weakened in the second stage of impact evolution.

Microseismic signals of double-layer hard and thick igneous strata separation and fracturing

In order to analyze the microseismic (MS) effects of hard and thick igneous strata separation and fracturing and the corresponding evaluation index of fracturing intensity, the temporal-spatial evolution of the MS sources generated by igneous strata fracturing in the 10416 working face of the Yangliu coal mine (YCM) was dynamically recurred, and the waveform and frequency-spectrum distribution characteristics of primary and igneous strata fracturing were clearly investigated, respectively. In addition, the relationship between the MS dominant frequency, the energy ratio in low-frequency band and the intensity of igneous strata fracturing was revealed, and the energy ratio of MS event in low-frequency band can be verified as an effective index for evaluating roof fracturing intensity. The work may put forward a certain reference for early warning and evaluating hard and thick roof fracturing and the induced coal-rock dynamic disasters based on in-situ MS observation.

Advanced Modeling of Interwell-Fracturing Interference: An Eagle Ford Shale-Oil Study

Summary To investigate interwell interference in shale plays, a state-of-the-art modeling workflow was applied to a synthetic case on the basis of known Eagle Ford shale geophysics and completion/development practices. A multidisciplinary approach was successfully rationalized and implemented to capture 3D formation properties, hydraulic-fracture propagation and interaction with a discrete-fracture network (DFN), reservoir production/depletion, and evolution of magnitude and azimuth of in-situ stresses by use of a 3D finite-element model (FEM). The integrated workflow begins with a geocellular model constructed by use of 3D seismic data, publicly available stratigraphic correlations from offset-vertical-pilot wells, and openhole-well-log data. The 3D seismic data were also used to characterize the spatial variability of natural-fracture intensity and orientation to build the DFN model. A recently developed complex fracture model was used to simulate the hydraulic-fracture network created with typical Eagle Ford pumping schedules. The initial production/depletion of the primary well was simulated by use of a state-of-the-art unstructured grid reservoir simulator and known Eagle Ford shale pressure/volume/temperature (PVT) data, relative permeability curves, and pressure-dependent fracture conductivity. The simulated 3D reservoir pressure field was then imported into a geomechanical FEM to determine the spatial/temporal evolution of magnitude and azimuth of the in-situ stresses. Importing the simulated pressure field into the geomechanical model proved to be a critical step that revealed a significant coupling between the simulated depletion caused by the primary well and the morphology of the simulated fractures within the adjacent infill well. The modeling workflow can be used to assess the effect of interwell interferences that may occur in a shale field development, such as fracture hits on adjacent wells, sudden productivity losses, and dramatic pressure/rate declines. The workflow addresses the complex challenges in field-scale development of shale prospects, including infilling and refracturing programs. The fundamental importance of this work is the ability to model pressure depletion and associated stress properties with respect to time (time between production of the primary well and fracturing of the infill well). The complex interaction between stress reduction, stress anisotropy, and stress reorientation with the DFN will determine whether newly created fractures propagate toward the parent well or deflect away. The technique should be implemented in general development strategies, including the optimization of infilling and refracturing programs, child well lateral spacing, and control of fracture propagation to minimize undesired fracture hits or other interferences.

Coupled disaster-causing mechanisms of strata pressure behavior and abnormal gas emissions in underground coal extraction

The generalization and application of fully mechanized caving with super great mining height (SGMH) face a series of new issues, of which strata pressure behavior and abnormal gas emissions are the most prominent disasters and display a close relationship. The Tashan coalmine was chosen as the experiment base because of its SGMH and the overlying hard and thick main roof (HTMR). This coalmine had experienced many damaging hydraulic support and abnormal gas emission accidents induced by strata pressure behavior. The “Key Strata Theory” and the fracture failure process analysis model established by 3DEC were used to analyze the structural characteristics and fracture failure process of the HTMR. The geostress reduction and permeability enhancement redistribution of the adjacent coal measure strata were studied by the geostress and permeability distribution model established by FLAC 3D. The HTMR controlled the failure extent and the movement evolution of the entire overburden stratum. The HTMR acted as a large double-sided embedded rock beam during primary fracturing and a cantilever-articulated rock beam during periodic fracturing, and it generated a huge hanging space above the gob. The fully mechanized caving with SGMH caused large-scale disturbances and permeability enhancements in the adjacent rock and coal strata. Then, the substantial amounts of gas stored in the remaining coal, surrounding rock strata and adjacent coal seam rushed out and aggregated in the caved and fissured zones of the gob, forming a huge gas warehouse. The strata pressure behavior and abnormal gas emission disasters primarily occurred after the primary and periodic fracturing of the HTMR. These disasters are predominantly caused by the escaping of the abundant gas that existed in the gob during mine pressure behavior processes. When the ultimate broken span was reached, as the HTMR rotated and collapsed, the substantial amounts of gas that accumulated in the gob escaped into the working face, which easily caused abnormal gas emissions. Hydraulic presplitting and gas drainage technologies are proposed to solve these disasters.

Garnets from diamond deposits in China and in the Arkhangelsk diamondiferous province

The morphology and chemical composition of garnets from principal deposits in China and in the Arkhangelsk Province consisting of kimberlites of various mineral types have been examined. The morphology of garnets (300 specimens) from the V. Grib pipe was examined, in which crystal fragments and irregular grains predominate, and dissolution traces are common. Distribution of types of garnet coloration is typical of kimberlites: lilac-violet and red garnets of ultramafic rock association are preponderant, and the proportion of yellow-orange garnets is rather high, while brown garnets are very rare. The garnet preservation degree is very low, which is related to their high primary fracturing due to cataclasis. Grains with finely matted surfaces are preponderant (90%) reflecting their high corrosion alterations. The chemical composition was determined in 56 garnet speciments from the Grib pipe. Garnets from lherzolitic and eclogitic rock types were found and garnets from magnesium and ilmenite ultramafics are present; there are no garnets from eclogites, but garnets from diamondiferous rock associations occur. The investigations demonstrated that garnets from lherzolite rock association are preponderant in kimberlites from China, as well as from other regions, while garnets from the harzburgite-dunite and from diamondiferous rock associations are rare. Garnets belonging to the graphitepyrope depth facies were also found.

OSTEOPOROSIS

Osteopenia, in the form of osteoporosis, is a common complication of chronic cholestatic liver diseases and, although its cause is poorly understood, it appears to be intimately related to the cholestasis itself. With more patients surviving longer with successful liver transplantation, the clinical significance of such osteopenia has increased, and a traumatic fracturing has become a major cause of morbidity in this patient population. Noninvasive diagnosis is easy, and serial measurements allow assessment of disease progression. Although no effective therapy can treat or prevent this complication, supportive measures can improve skeletal well-being, especially in high-risk individuals who are candidates for liver transplantation.

Hydrocarbon Trap Types and Deformation Styles Modeled Using Quantified Rates of Salt Movement, Louisiana Margin

ABSTRACT Definitions are proposed for the various salt features along the Louisiana continental margin. The nine general features include salt wedges, salt tongues, pillows, diapirs, wings, canopies, sheets, sills, and dikes. The definitions are derived from the interpreted salt geometry and contain an implied genesis. These definitions are here proposed with the hope of promoting a dialogue to result in a suite of accepted definitions. Movement of salt appears to result from the confining pressure of sediment deposition. Deposition is controlled by sealevel oscillations, subsidence, and source. Salt movements include lateral flow, buoyancy, and isostacy. Lateral flow may occur under the Louisiana shelf-break, terminating basinward at the present Sigsbee Escarpment; isostacy may occur under the upper- middle slope and outer shelf. Buoyancy appears to be dominant under the middle and inner shelf, coastal plain, and South Louisiana and Northern Louisiana-Arkansas interior basins. Calculated rates of salt motion apparently may range from as high as 17cm/yr (salt wedge migrating during Plio-Pleistocene only during lowstands) to as low as cms/1000 yrs (salt pillows under the inner shelf, coastal plain, and interior basins). Given these calculations, it has been possible to prepare computer-derived plots of fracturing models around the various salt features. Salt movements from 10-100 m/m y up to 10-200 km/m y have been modeled, using Mohr's criterion for failure, in order to examine the domains of primary and secondary fracturing around salt bodies. The results of modeling show that (1) the higher the rate of salt motion, the larger the range of fracturing; (2) the domain of fracturing increases with larger size and with faster migration. For large, high speed salt features, the fracturing domain apparently extends as far as 2-4 km in the vertical and 3-5 km in the lateral directions.

Modeling Salt Tectonic Evolution and Sedimentary Fracturing along Northern Gulf of Mexico

Massive hydrocarbon reservoirs associated with salt features along the northern Gulf of Mexico prompts interest into the synergistic and dynamic evolution of the two features. Use of geologic models from the evolution of salt movement in the northern gulf provides constraints on movement rates. Salt originally deposited some 150 Ma on continental crust, i.e., South Louisiana basin, migrating to present position along Sigsbee Escarpment, would, on average, move at 0.3 cm/yr; or, if movement occurred only during lowstand, at 0.5 cm/yr. If extruded salt lay along present shelf-break during Upper Miocene-Pliocene (10 to 2.5 Ma), then the extrusion rate would be, on average, 7 cm/yr and, during lowstand only, 17 cm/yr. Under the slope, salt is suggested to respond isostatically to new deposition, yielding a vertical migration rate of cms/yr, given sedimentation rates of a kilometer per single fourth order (Milankovitch) lowstand. Under the shelf, buried salt apparently moves by buoyancy at cms/1000 yrs. Given this model for salt tectonic rates, it is possible to examine domains of primary and secondary fracturing, using Mohr's criteria for failure, surrounding salt features of the Louisiana offshore. It is shown that (1) the higher the rate of salt motion, the larger the range more » of fracturing; (2) the domain of fracturing around salt features depends on salt size, sediment properties, and salt speed. Generally the fracturing domain extends 2-4 km in the vertical direction, and 3-5 km in the lateral direction. « less

Modeling Fracturing and Faulting Within Sediments Around Rapidly Moving Lateral Salt Sheets (1)

Numerical modeling of high-speed motion of salt sheets at various rates (50-150 km/m.y.), depths, and salt sheet thicknesses through sediments is illustrated in this study. Mohr's criterion for failure is used to examine the domains of primary and secondary fracturing in formations surrounding the salt body. Deformations of sediments are also displayed. It is shown that (1) the higher the rate of salt motion, the larger the distance range of fracturing away from the advancing tip, and (2) the domain of fracturing around the salt body depends on the salt size and sediment properties as well as on the salt speed. Generally the fracturing domain extends as far as 2-4 km in the vertical, and to about 3-5 km in the lateral directions from the tip. Several inferences from the m deling results may be of significance in attempts to evaluate hydrocarbon proneness of formations in association with salt sheets.