Lateral Permeability Research Articles

Isotopic imaging of surface water/groundwater interactions, Sacramento Valley, California

Groundwater isotope data across the Sacramento Valley, California establish two types of groundwater mining: (1) overdraft of ancient groundwater with limited recharge by surface waters, producing cones of depression; (2) ancient groundwater withdrawal followed by rapid recharge of irrigation water, reducing groundwater quality. The first type occurs in the Sacramento metropolitan area, where meteoric runoff is unnaturally high and 40 years of pumping have depressed water levels to 25 m below sea-level, inducing recharge from losing reaches of the Sacramento and American rivers. Lateral migration rates are quantified by the binary mixing between river water (δ18O = −10.8) and natural groundwater (δ18O = −7.0). The second type of mining occurs in agricultural regions to the west, where 14C ages indicate that irrigation waters constitute more than 80% of modern recharge. This recharge has several characteristics of evaporated irrigation water, including: (1) high δ18O values (to > −6.0) that define closed contour patterns; (2) elevated NO3 concentrations (to 100 ppm); (3) low 14C ages of less than 500 years.Stable isotope contours, augmented by 14C data, provide dynamic recharge patterns in this profoundly disturbed, giant alluvial aquifer. On a large scale (> 100 km2), the lateral permeabilities of alluvial aquifers are essentially isotropic, whereas on a smaller scale (< 25 km2), anisotropy is evident and isotope values can be geographically complex and seasonally transient. Groundwater flow patterns implied by the isotope data can differ substantially from steady-state models based on head measurements.

Geostatistical Models of Secondary Oil Migration Within Heterogeneous Carrier Beds: A Theoretical Example

This paper critically evaluates the utility of two different geostatistical methods in tracing long-distance oil migration through sedimentary basins. Geostatistical models of petroleum migration based on kriging and the conditional simulation method are assessed by comparing them to known oil migration rates and directions through a numerical carrier bed. In this example, the numerical carrier bed, which serves as ground truth in the study, incorporates a synthetic permeability field generated using the method of turning bands. Different representations of lateral permeability heterogeneity of the carrier bed are incorporated into a quasi-three-dimensional model of secondary oil migration. The geometric configuration of the carrier bed is intended to represent migrat on conditions within the center of a saucer-shaped intracratonic sag basin. In all of the numerical experiments, oil is sourced in the lowest 10% of a saucer-shaped carrier bed and migrates 10-14 km outward in a radial fashion by buoyancy. The effects of vertical permeability variations on secondary oil migration were not considered in the study. Two sets of numerical experiments are presented in this study. In the first set, computed oil migration patterns and rates through the numerical carrier bed are compared to kriged and optimal estimations based on a suite of 50 conditional simulations to determine the utility of each geostatistical approach. The geostatistical models also are compared to a much simpler oil migration simulation using a homogeneous carrier bed, an assumption typically made in cross sectional models of oil migration. The permeability realizations generated by kriging and the conditional simulation method were constructed using 50 randomly placed sampling points. A second set of numerical experiments was made to determine how data sample size (20, 35, 50, 100, and 250 randomly selected points) influences p edicted oil migration patterns using kriged permeability fields. Oil migration patterns through the synthetic carrier bed were quantitatively compared to geostatistical representations of oil transport by computing the degree of correlation (r2) of oil lens thickness at 5, 10, and 15 m.y. after the onset of migration. Quantitative results indicate that both kriging and the conditional simulation method produced realistic representations of spatial oil lens patterns and first arrival times. Both kriging and the conditional simulation method produced results far more realistic than the simulation with a homogeneous carrier bed. After 15 m.y., the spatial correlations (r2) between the known oil lens patterns and that of the kriged and ensemble average of the 50 conditional simulations were 0.67 and 0.74, respectively. Although the conditional simulation method produced the best results, it did so at a significant computational expense. Computed oil migration patterns based on different kriged permeability maps that incorporated varying amounts of control data points did not improve signif cantly when more than 100 randomly placed wells were used. The study provides compelling evidence that secondary oil migration is an inherently three-dimensional process. For well-studied basins, geostatistical representations of long-range oil migration could be of value in ongoing exploration strategies. End_Page 1679------------------------------

Geophysical evaluation of sandstone aquifers in the Recôncavo‐Tucano Basin, Bahia—Brazil

The upper clastic sediments in the Recôncavo‐Tucano basin comprise a multilayer aquifer system of Jurassic age. Its groundwater is normally fresh down to depths of more than 1000 m. Locally, however, there are zones producing high salinity or sulfur geothermal waters. In other areas, the system is being exploited heavily to support a petrochemical center and related industries. Analysis of electrical logs of more than 150 wells enabled the identification of the most typical sedimentary structures and the gross geometries for the sandstone units in selected areas of the basin. Based on this information, the thick sands are interpreted as coalescent point bars and the shales as flood plain deposits of a large fluvial environment. The resistivity logs and core laboratory data are combined to develop empirical equations relating aquifer porosity and permeability to log‐derived parameters such as formation factor and cementation exponent. Temperature logs of 15 wells were useful to quantify the water leakage through semiconfining shales. The groundwater quality was inferred from spontaneous potential (SP) log deflections under control of chemical analysis of water samples. An empirical chart is developed that relates the SP‐derived water resistivity to the true water resistivity within the formations. The patterns of salinity variation with depth inferred from SP logs were helpful in identifying subsurface flows along major fault zones, where extensive mixing of water is taking place. A total of 49 vertical Schlumberger resistivity soundings aid in defining aquifer structures and in extrapolating the log derived results. Transition zones between fresh and saline waters have also been detected based on a combination of logging and surface sounding data. Ionic filtering by water leakage across regional shales, local convection and mixing along major faults and hydrodynamic dispersion away from lateral permeability contrasts are the main mechanisms controlling the observed distributions of salinity and temperature within the basin.

Exploration and Development of Ground Water from the Stone Forest Karst Aquifers of South China

AbstractStone forest aquifers are the most widely exploited sources for ground water in the vast south China karst belt. These aquifers occupy a thin epikarst zone that has been infilled with clastic sediments. The aquifers are characterized by large lateral permeabilities and small reservoir capacities owing to their thinness. The carbonate rocks which comprise the framework for the aquifers are usually buried under the karst plains and large karst depressions where development is desired.The stone forest aquifer exploration procedure must first locate saturated zones. Second, those parts of the saturated zone having the greatest dissolution porosity must be identified because the infilled dissolution voids contain the water.The best indicators of saturation include the combination of low topography and the presence of active karst features such as springs, karst windows (natural openings exposing the water table), and live surface streams. These elements are readily observed on intermediate scale (1:20,000) aerial photography.The depth and degree of carbonate dissolution porosity is a function of several geologic and hydrologic factors including carbonate rock type, carbonate purity, fracture density, specific discharge, age of the circulation system, etc. These variables cannot be measured directly because the carbonate rocks are usually buried under a thin mantle of clastic sediments. However, if it is recognized that the ground‐water system has already exploited the most favorable geology and that dissolution is an ongoing process, a simple indirect method can be used to identify the areas having the greatest porosity. The presence of karst depressions and recent sinkholes are indicative of the most intensely karstified and hydraulically active parts of the epikarst zone. Mapping of these surface features from stereo aerial photography is a simple geomorphology exercise that can be used to directly identify the most favorable well sites.Current well construction practices in the south China karst belt involve both dug and drilled wells. Dug wells are preferred in many locations owing to both cost‐effectiveness associated with cheap labor and lack of available drilling equipment. The dug wells look and function identically to karst windows and thus conform to timeless water use traditions in the region.

Hydrogeologie Characteristics and Deforestation of the Stone Forest Karst Aquifers of South China

AbstractStone forest aquifers comprise an important class of shallow, unconfined karstic aquifers in the south China karst belt. They occur under flat areas such as floors of karst depressions, stream valleys, and karst plains. The frameworks for the aquifers are the undissolved carbonate spires and ribs in epikarst zones developed on carbonate strata. The ground water occurs within clastic sediments which infill the dissolution voids.The aquifers are thin, generally less than 100 meters thick, and are characterized by large lateral permeabilities and small storage. The result is that the aquifers are difficult to manage because recharge during the rainy season moves rapidly out of the aquifers. Water levels fall sharply as the dry season progresses and the ground‐water supply falls off accordingly.The magnitude and duration of the seasonal recharge pulse that replenishes the stone forest aquifers have been severely impacted by massive post‐1958 deforestation in the south China karst region. Water that was formerly retained beyond the wet season in the forested uplands, later to be released to the stone forest aquifers under the lowland plains, now passes quickly through the system during the wet season. The loss of this seasonal upland storage has resulted in both a reduction in the volume of recharge to the lowland stone forest aquifers and a shortening of the seasonal recharge event. The result is accelerated water‐level declines in the stone forest aquifers as the dry season progresses which, in turn, causes premature dewatering of wells and decreased spring discharges. This response is compounded by increased ground‐water withdrawals as the people attempt to offset the declining supply. Management of the total water‐supply system requires not only tinkering with the aquifer, but massive reforestation efforts to restore dry season water retention in the upland parts of the watersheds.

Outcrop Quantification of Flow-Unit and Seal Properties and Geometries, Ferron Sandstone, Utah

River-dominated deltaic sandstones of the Upper Cretaceous Ferron Member of the Mancos Shale provide the opportunity to quantify the 3-D architecture and permeability structure of fluvial, deltaic, and shorezone sandstones that are analogous to large oil and gas reservoirs of the Gulf Coast. Current investigations, working within a previously established stratigraphic framework, are aimed at quantifying flow-unit character as well as delineating bounding and sealing surfaces that cause inefficient drainage and the abandonment of conventionally recoverable hydrocarbons in reservoir analogs. Measured sections at 1-mi spacings establish the facies framework within which windows are selected for detailed study. Average permeabilities are highest in distributary-channel facies. Distributary sandstones are, however, also characterized by the highest degree of permeability heterogeneity. Lateral permeability heterogeneity, a response to lateral accretion and channel-flooring scours, is pronounced. In contrast, associated shoreface sandstones have lower average permeabilities, simple upwardly increasing permeability profiles, and a high degree of lateral continuity. Vertical heterogeneity, provided by laterally continuous mud layers, is dominant. Communication between distributary channel and associated shoreface sandstones is likely to be hindered by low-permeability (less than 5 md) zones that consistently occur at the base of channel sandstones and along the toesets of lateral accretion surfaces.

Sequential Steam: An Engineered Cyclic Steaming Method

"The Potter Sand... has responded well to virtually all thermal recoverymethods... Cyclic steam, however, has been the best EOR process for selectedleases." Summary Cyclic steam injection has been the most widely used EOR method in areas ofthe Potter sand in the Midway-Sunset field, Kern County, CA. This paperdiscusses the field pilot and the statistical and theoretical studies leadingto the design of a sequential steaming process, plus the implementation of thisprocess on three leases. Introduction Oil is produced from many different sands in the Midway-Sunset field, andthermal EOR is the predominant recovery method. The Potter sand. the mostprolific reservoir in the field. has responded well to virtually all thermalrecovery methods. including steamdrive, in-situ combustion. and cyclic steamstimulation. Since the early 1960's, Santa Fe Energy Co. has experimented withall these methods in the Potter sands with varying degrees of success. Cyclicsteam, however. has been the best EOR process for selected leases. Indeveloping our cyclic steam technique. we devised a method called"sequential steam that we feel is a superior way to process these thick, steeply dipping, heavy-oil sands. Geology The Potter sands. the primary producing zones in the northern end of theMidway-Sunset field (Fig. 1), are in the upper portion of the Reef Ridgeformation of Late Miocene Age. According to Lennon, the sands are predominantlya series of fan-channel complexes formed during rapid subsidence of the basin. Coarse granitic debris from the coastal range flowed down marine canyons into adeepwater fan. The depositional character of the Potter is extremely variable, ranging from massive, conglomeritic. debris-flow-filled, narrow channels tothinly bedded, laterally extensive, very-fine-grained, distal-fan turbidites. The subsidence produced a generally transgressive sequence; that is, thedeeper-water. thinly bedded deposits tend to overlie stratigraphically thecoarser, shallow-water channels. Subsequent uplift and tilting produced anerosional surface upon which the Pleistocene Age lacustrine and alluvial-fanTulare formation was deposited. The final uplift and erosional sequence leftthe Potter sands in the setting shown in Fig. 2. The producing sands outcrop atthe western limit of Potter production and are covered by a rapidly thickeningwedge of Tulare silts and sands toward the east. Dips range from about 40 atthe west to 20 at the east and trend north to east. Net sands also are highlyvariable. In the northwestern region of Potter production, especially in the 21Fee lease (see Fig. 1 for all lease locations), where the deposition ispredominantly debris-filled channels. The few existing permeability barriersare discontinuous (presumably caused by channel scour) and often will notcorrelate along strike from one well location to the next. Consequently, netsand counts range up to 700 ft, with as little as 50 ft of shale intervals. Thedeltaic distal-fan deposits to the east are finely interbedded sands and shaleswith individual members ranging in thickness from inches to tens of feet. Netsands may total less than 100 ft in a gross interval of 200 Common reservoir properties in these leases are low-gravity crude (11.5 to13 API). fairly steep dips, good lateral permeability between well locations, low water cuts (~40%). an inactive aquifer. and a reservoir mineralogyapparently highly resistant to damage by steam. History Upstructure Potter Sand Steamflood Pilots. Santa Fe began cyclic steamoperations in the Midway-Sunset field in early 1964. Well No. 36, 27 USL lease, was steamed with a 150-psi tank heating boiler. That first cycle experiencedpeak oil rates of nearly 200 B/D and convinced us that steam was a veryattractive EOR method in this reservoir. The first steamdrive in the area ofinterest began in Aug. 1967. Pilot 201–27 Fee was a single inverted five-spot(see Fig. 1) in an upstructure attic location. Unfortunately. as shown in Fig.3, the project performed poorly, with an instantaneous incremental steam/oilratio (SOR) of more than 9 bbl/bbl [fuel/oil ratio (FOR) of 0.73] during itsbest performance in 1969 and 1970. Cumulative incremental SOR performance wasabout 17 bbl/bbl (FOR of 1.3). Note that once steam decreased to a ratecommensurate with the observed production rate, all response was lost. Apostaudit of this drive showed conclusive evidence of uncontrolled steam lossto the upstructure air zone, which is laterally unbounded for all practicalpurposes. JPT P. 848⁁

Depositional Environments, Sequence Stratigraphy, and Trap Configuration of Lower Wolfcampian Clastics Along Eastern Edge of Midland Basin, West Texas: ABSTRACT

The Lower Permian (lower Wolfcampian) along the eastern edge of the Midland basin, west Texas, is characterized by ramp-type shelf margins. During eustatic lowstand, nearshore sedimentation shifted drastically to the west into a basinal setting below the Pennsylvanian (Canyon) shelf margin. Core descriptions demonstrate that lowstand systems tract (LST) and transgressive systems tract (TST) siliciclastics were deposited in deltaic and coastal-plain environments. Prodelta, delta-front, and stream-mouth bar facies are associated with the LST. Coastal-plain and distributary channels are preserved in the TST. The sequence stratigraphic framework indicates type 1 sequence boundaries at 287 Ma, 282 Ma, and 280 Ma in the lower Wolfcampian clastics. This lower Wolfcampian package of sedimentary rocks overlies the Pennsylvanian and is capped by the 279-Ma middle Wolfcampian unconformity. All three sequence boundaries and associated systems tract deposits exhibit a prograding stacking pattern within the sequence stratigraphic framework. Basinally restricted prograding LST deltaic rocks are overlain by backstepping TST deltaics and highstand systems tract (HST) outer marine shales. Production in lower Wolfcampian clastic fields is associated with fine-grained quartzarenites up to 45 ft thick which were deposited in stream-mouth bars. Delta-front and prodelta low-permeability shales encase the reservoir facies, forming lateral permeability barriers. HST outer marinemore » shales deposited over the stream-mouth-bar sandstones act as a top seal, creating a stratigraphic trap and providing source for the high-BTU gas and oil produced from these basinally restricted LST deltaics.« less

Determination of fluid flow properties from the response of water levels in wells to atmospheric loading

The water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading. The magnitude and character of this response is partly governed by the well radius, the lateral hydraulic diffusivity of the aquifer, the thickness and vertical pneumatic diffusivity of the unsaturated zone, and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer. These key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response. In many cases, the response of a well to atmospheric loading can be broken up into a high‐, intermediate‐, and low‐frequency response. The high‐frequency response is governed largely by the well radius and lateral diffusivity of the aquifer. The intermediate‐frequency response is governed by the loading efficiency of the aquifer. The low‐frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer. Cross‐spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters. These estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone, the lateral permeability of the aquifer, and the composite vertical hydraulic diffusivity of the overlying saturated materials.

Appraisal of Woven Fabric Performance

This work evaluates the performance of 100% cotton woven fabrics. We have ex amined abrasion resistance, diverse mechanical properties (compression and flexion), and certain aesthetic properties (handle, i.e., stiffness, smoothness, and softness). Changes in the properties of a fabric as a consequence of wear are illustrated; wear is a laboratory action involving some method of abrasion such as an Accelerotor on either dry or damp fabrics. In addition, we consider some aspects of the physical and mechanical properties of woven fabrics in which changes in weight, thickness, stiffness, air permeability, and compression are used as criteria to assess damage caused by frictional abrasion. The results show that weight loss may be small as a result of short periods of accelerated wear, and changes in other physical properties may be large, particularly compression, flexion, and air permeability. The differences between worn and unworn fabrics can be detected subjectively by touch. Changes occur in fabric properties as a result of incremental wear. Weight per square meter, coercive couple, and flexural rigidity show consistent decreases with increasing abrasion time at a fairly uniform rate. Thickness, air permeability, lateral air permeability, and compression show inconsistent increases with increasing abrasion time at non-uniform rates.

A digital simulation model for the unsteady-state radial flow to a dug well

A digital simulation model has been presented for the solution of the unsteady-state radial flow to a large-diameter dug well perforating the full saturated thickness of an unconfined aquifer. The numerical solution is based on the finite difference approach. The computational algorithm is an iterative version of the alternating direction implicit method. The time variant discharge from the aquifer, and the reduction in saturated thickness due to water withdrawal during both the abstraction and recovery phases have been suitably incorporated in the simulation model. A sensitivity analysis has been carried out on the model parameters of the aquifer, namely lateral permeability, anisotropy, specific storage and specific yield. The results indicate that the model response of hydraulic heads in the aquifer is mainly sensitive to variations in lateral permeability and specific yield alone. The simulation model has also been applied to analyse data from well pumping tests. The particular combination of parameters characterizing the aquifer at the test-site have been identified by a parameter adjustment procedure.

A model of regional fluid flow: Sand concentration factors and effective lateral and vertical permeabilities

Permeabilities of sand and shale differ by five to seven orders of magnitude. In the depositional pattern characteristic of the Gulf Coast, lenticular sand bodies occur randomly dispersed within a shale matrix, even though they can be grouped into stratigraphic sequences, contributing to net permeability of the sand-shale system and thus facilitating upward flow of pore water. In addition, a substantial lateral flow develops as fluid flow is directed toward sand bodies, thus concentrating fluid from a wide source area into sand bodies of limited lateral and vertical extent. Calculations reported here determine the effect of randomly distributed sands on both vertical and lateral permeabilities of composite sandshale systems. Effective permeabilities depend only on mean sand percent and local variance about the mean, because the effects of sand body shapes and their orientation and dip are not incorporated in the analysis. Results indicate that at a mean sand percentage of 20–50% a large lateral migration of fluid flow develops as sand bodies attract flow from a region two to seven times the radius of the sand body itself. For a mean sand percentage in excess of 50–60%, large vertical migration results and thus hydrocarbon trapping should not be expected for sand percentages in excess of 50–60%. Results of these calculations are in accord with observations that most larger oil accumulations on the Gulf Coast are found in regions having sandiness between about 20 and 50%.

Stratigraphy, Depositional History, and Trapping Mechanisms of Lone Tree Creek and Lodgepole Creek Oil Fields, Lower Cretaceous Fall River Formation, Powder River Basin, Wyoming: ABSTRACT

Stratigraphically trapped accumulations of oil in the Lone Tree Creek and Lodgepole Creek fields occur within and just updip from a fluvial meander belt within the Fall River Formation. The meander belt can be mapped north-to-south over a distance of at least 100 mi (161 km) in the eastern part of the Powder River basin. The northern part of the meander belt contains the oil fields of the Coyote Creek-Miller Creek trend; the southern part contains only the relatively small Lone Tree Creek and Lodgepole Creek fields. These small fields are of considerable interest, as they display a style of stratigraphic trapping of hydrocarbons not observed in the prolific Coyote Creek-Miller Creek trend. The stratigraphic traps of the Coyote Creek-Miller Creek trend occur at updip-facin convexities along the eastern edge of the meander belt, with abandonment clay plugs serving as lateral permeability barriers to hydrocarbon migration. Oil has been produced in part of the Lone Tree Creek field from a similar trap. The remaining part of Lone Tree Creek field and Lodgepole Creek field produce from stratigraphic traps formed by lateral pinch-outs of delta-front sandstone bodies. These traps are situated updip from and apparently in continuity with the meander-belt deposits, indicating that they may have been charged with hydrocarbons that found their way through the clay-plug barriers along the margin of the meander belt. Similar, undiscovered traps may exist updip from Fall River meander belts elsewhere in the basin. End_of_Article - Last_Page 850------------

Facies Control on Oil Production From Upper Member of Permo-Pennsylvanian Minnelusa Formation, Powder River Basin, Wyoming: ABSTRACT

Lateral and vertical facies variations within the predominantly eolian upper member of the Minnelusa Formation control both the regional reservoir distribution and the localization of oil-producing trends. Sands sourced by northeasterly trade winds were deposited in a land area bounded on the west by the Lusk embayment, which was a shallow, restricted extension of the Permo-Pennsylvanian sea. This embayment was present throughout Minnelusa deposition, and was located in the western portion of the present-day Powder River basin. Another extension of the epeiric sea, located in western South Dakota, formed the eastern boundary of the land area. In the northern part of this area, an inland sand-sea developed; in the southern part, the sand supply was less and isolated barchan dunes migrated over a coastal sabkha. Dune sandstones are bounded laterally by predominantly sandy interdune deposits in the north and by coastal interdune deposits, including sandstone, dolomite, and anhydrite, in th south. Major marine transgressions deposited laterally extensive dolomites that separate the dune sandstones. Interdune deposits constitute permeability barriers adjacent to dune sandstones. The dune sandstones, which can be of excellent reservoir quality, were subjected to early cementation by anhydrite. Later dissolution of the anhydrite cement, facilitated by good to excellent sorting and possibly enhanced by hydrocarbon migration, led to development of significant secondary porosity. Interdune sandstones are less well sorted and so did not develop good secondary porosity. Interdune carbonates and evaporites have virtually no permeability. The coastal interdune deposits in the southern part of the region, therefore, form more effective lateral permeability barriers than do the sand-dominated interdune deposits in the north. End_of_Article - Last_Page 852------------

Effect of Flow Time Duration on Buildup Pattern for Reservoirs With Heterogeneous Properties

Abstract For a heterogeneous reservoir, the shape of a buildup curve is strongly dependent on the length of the preceding flow period. Therefore, in exploration well testing, where the flow period is usually short, modification of the pressure buildup pattern caused by insufficient flow time can lead to erroneous interpretation of well behavior. Buildup pattern, as a function of flow time, is discussed here for various types of ideal heterogeneities such as linear reservoir discontinuities, natural fractures, vertical stratification, pressure support, and lateral permeability loss. A relationship is provided for the dimensionless flow time required to produce a certain buildup pattern. The effect of flow time on quantitative assessment of reservoir parameters is determined as well.

Analysis of dug-well test data

This paper is concerned with the analysis of test data from dug wells. A mathematical model is presented with the boundary condition along the well face being defined on the basis of alternative assumptions made on how the radial hydraulic gradient is distributed over the well face. Approximate equations for the recovery phase are obtained based on an additional assumption that the radial hydraulic gradient along the well face is linearly related to the drawdown in the dug well. The use of these equations leads to the determination of a parameter of the form P r B (where P r is the lateral permeability of the aquifer and B is a constant) and of the time required for the dug well to recoup fully. A simple field test procedure is adopted to obtain conditions of different discharges from the well and an empirical relationship between the parameter P r B and the well discharge is established for the test well site. The approximate equations that are developed also find use in correcting some of the common anomalies in the abstraction phase data.

Deposition and Diagenesis of Glauconite Sandstone, Berrymore-Lobstick-Bigoray Area, South-Central Alberta: ABSTRACT

The depositional environments of the Glauconite sandstone in the Berrymore-Lobstick-Bigoray area are distributary channels, delta platform, distributary mouth bars, and interdistributary bays. The diagenetic mineralogy is consistent with the formation water chemistry . A simplified model for evolution of Glauconite sandstone water compositions includes (1) original derivation in a deltaic setting giving composition of early pore waters as brackish to normal marine, (2) alteration due to inorganic and organic chemical diagenesis, and (3) dilution through time due to meteoric water recharge. The formation waters now evolved have such a composition as to be (1) oversaturated with respect to hematite, kaolinite, and illite (late-stage cements); and (2) near equilibrium to undersaturated with respect to quartz, calcite, siderite, and dolomite. The early diagenetic mineralogy is a function of early pore waters and thus the subenvironment. For example, ankerite cement forms early at the base of distributary channels. The intermediate to late diagenetic cementation is a function of early diagenetic mineralogy. For example, hematite is formed by the oxidation of siderite due to meteoric water recharge. Oxidation of pyrite is quantitatively unimportant. Occurrence of late stage hematite is associated with structural highs which are most affected by meteoric water recharge. Delta platform deposits contain gas, and distributary channel and distributary mouth bar deposits contain water. Delta platform deposits are isolated from distributary channel and distributary mouth bar deposits by a vertical permeability barrier of ankerite cement and a lateral permeability barrier of siderite and kaolinite cement, respectively. End_of_Article - Last_Page 606------------

Type‐Curve Analysis of Time‐Draw down Data for Partially Penetrating Wells in Unconfined Anisotropic Aquifers

ABSTRACTWith the aid of a computer, and using an iterative alternating‐direction implicit method, a numerical solution is sought for the unsteady‐state radial flow to partially penetrating wells pumping at a constant rate from an unconfined anisotropic aquifer. These solutions are used to generate a series of theoretical type curves valid for individual aquifer‐test situations characterized by particular combinations of two constants Q = (Pr/Pz) (m/rw)2 and C2= (Sy/Ssm) and particular well penetration. The aquifer‐test data requirements are the time‐drawdown data and at least two pairs of observation wells, one of the pair tapping well‐screen depths and the other tapping water‐table depths. The parameters that are identified are the lateral permeability, vertical permeability, specific storage and specific yield of the aquifer. The use of the type curves is illustrated by an example.

Digital model studies of unsteady-state radial flow to partially penetrating wells in unconfined anisotropic aquifers

A digital model solution is sought for the unsteady-state radial flow to a partially penetrating well pumping at a constant rate from an unconfined anisotropic aquifer. The solution technique used is the iterative alternating-direction implicit method. Attention is focused on the utility of the digital model to analyse aquifer test-data in unconfined aquifers, so as to evaluate the lateral permeability, vertical permeability, specific storage and specific yield of the aquifer. That an approximate steady-state solution of flow to partially penetrating wells in unconfined aquifers can be sought is also illustrated. The digital model is applied to analyse field aquifer test-data of the time distribution of average drawdown at well screen depths, and of water-table drawdown at two radial distances from the test-well.

Digital Model Studies of Steady‐State Radial Flow to Partially Penetrating Wells in Alluvial Plains

ABSTRACTA digital simulation model for the steady‐state radial flow towards partially penetrating wells in the alluvial plains is presented. As the deposits in these plains are heterogenous with several good water‐bearing formations crisscrossed with silty layers, the deposits are treated as a single anisotropic aquifer with water‐table conditions prevailing. The iterative alternate direction implicit technique is used for the solution of the steady‐state flow. The digital simulation model is used to study the effects of anisotropy, screen setting, and screen length on the discharge per unit length of screen; and in evaluating the errors involved in determining lateral permeability from distance‐drawdown data. The digital simulation model is applied to field pump‐test data for purposes of identification of aquifer anisotropy and radius of influence of well, and in evaluation of errors in determining lateral permeability from distance‐drawdown data.