Subtraction of the two components (baseline and stimulation) of a neuroactivation study using 99Tcm HMPAO SPECT requires accurate registration of the two images. Immobilization of the subject during and between the two components of the study can prove difficult and degrades signal to noise ratio. The use of an automated image registration technique for registering the two components of the test can, even in the case where the subject is removed from the scanner, produce significantly better registration than immobilization.
Relationships of permeability to porosity are shown from analyses of more than 2,100 core plugs from nine wells in the Travis Peak, a low-permeability, tight-gas sandstone formation in northeast Texas. Effects of reservoir vs. ambient stress are shown for permeability, porosity, and the Klinkenberg factor. The relationship of brine permeability to gas permeability is also shown.
The incidence and severity of cognitive deficits after surgery for aneurysmal subarachnoid haemorrhage and their relationship to aneurysm site remains controversial. The aim of this study was to investigate the pattern of regional cerebral blood flow which exists in patients one year post-surgery and to identify whether different patterns exist which may be related to the type of cognitive deficit or the location of the aneurysm. 62 patients underwent cognitive assessment and HMPAO SPECT imaging at a mean time of 12 months following surgery. Results were compared to those from healthy control subjects (n = 55 for neuropsychological testing; n = 14 for SPECT imaging). In the patient group, significant stable cognitive deficits occurred in all cognitive domains but no cognitive measure differentiated aneurysm site. On SPECT images, statistical parametric mapping identified a large common area of subcortical hypoperfusion in the patient group as a whole. The findings of this study suggest a possible link between reduced subcortical function and the extent and severity of cognitive deficits.
A combination of new tools, the Digital Sonic and the Induced Gamma-Ray Spectroscopy (GST*) with the High Resolution Dipmeter (HDT*), a SARABAND* suite of logs. and a rock core study provided a unique opportunity to re-examine fracturing (fracing) procedures and producibility in the "tight gas sands" of the Cotton Valley Group in East producibility in the "tight gas sands" of the Cotton Valley Group in East Texas. The depositional paleo environment of the Cotton Valley tight gas sandstones is interpreted as a sequence of shallow, marine, organically-burrowed, shoreface deposits which, with the HDT, can be separated into sedimentation units—barrier bars or tidal deltas. This separation is important because the local feature, the tidal delta, may have a more limited reservoir than the massive sand unit, the barrier bar. The Digital Sonic tool measures values of shear and compressional velocities from which Poisson's ratio is determined. These velocities in combination with bulk density yield Young's Modulus which is commonly used to calculate fracture width. Combining Poisson's ratio with SARABAND provides answers needed to determine the vertical containment boundaries of the hydraulic fracture. The GST provides a lithological description which identifies hydrated shales and well-developed intergranular pore-filling cements such as quartz, calcite, and clay minerals which, in some cases, are containment boundaries. Producibility is then estimated as a function of the fracture surface area (fracture length x height) and the hydrocarbon pore volume (calculated from the SARABAND listing). This estimate of producibility is compared to flowmeter results. In several studies, the producibility is compared to flowmeter results. In several studies, the comparison is good; however, some significant, yet foreseeable, exceptions occur. Introduction Low porosity and low permeability sandstones, generally referred to as "tight gas sands", are reasonably common throughout the world. In the United States and Canada, five discrete tight sand gas basins occupy a north-south trending zone from Alberta to Colorado in rocks of Cretaceous to Tertiary in age. In addition, there are three low permeability zones of tight gas sands which lie outside this region: the permeability zones of tight gas sands which lie outside this region: the Oklahoma-Arkansas' Ouachita Mountain province (Mississippian), Texas' Sonora basin (Pennsylvanian), Arkansas-Louisiana-Texas' Cotton Valley trend (Jurassic) (Figure 1). Generally, tight gas sands have gas-filled porosities of 3 to 9% and in-situ gas permeabilities of 1 to 50 mu d. Shallow gas basins have exceptionally higher porosities and permeabilities - up to 14% and 1,000 to 10,000 /mu d, respectively. For permeabilities - up to 14% and 1,000 to 10,000 /mu d, respectively. For comparison, the tight gas sands of the Cotton Valley Group have gas- filled porosities in the range of 4 to 5% and permeabilities of 3 to 30 mu d. Using advanced recovery techniques in tight gas sands, it is estimated that the ultimate recovery may be as high as 0.18 × 10 Mcf with a value of $0.5 × 10 at $3/Mcf (Kuuskraa et al, 1978). The energy shortage, coupled with gas deregulation and the significant gas supply found in tight gas sands, initiated intense exploration activity in these unique sandstones. Schlumberger-Doll Research (SDR) in Ridgefield, CT and Schlumberger Well Services (SWS) in Houston. TX in cooperation with Delta Drilling Company (DDC) in Tyler, TX coordinated a broad study of a cored well, Alice Snider No. 1 (Figure 2), in a major tight gas sand field, the Carthage Field, about 60 miles east of Tyler, TX. The Carthage Field was a particularly good choice for this study. It is one of the major gas areas in North America - 48 miles tong in a southeast-northwest direction with a maximum width of 24 miles (Rogers, 1968). Also, there has been increased drilling activity in the Cotton Valley Group. For example, in the first quarter of 1980, about 29 wells were drilled; two were dry holes. In the same period in 1979, only 15 wells were completed. It is also worth noting that there were a number of wildcat locations outside of the established Cotton Valley trend, i.e., outside of Panola and Harrison Counties and into adjacent Rusk, Cherokee, and Panola and Harrison Counties and into adjacent Rusk, Cherokee, and Gregg Counties. The major effort of this cooperative study was to provide an environment to test a variety of standard (DIL*/BHC, GR/CNL*/FDC*, HDT/FIL*) and prototype (Digital Sonic, CNL-G, EPT*, GST-A, NGT*, NML*) tools against a rock core examined at both the macro- and microscopic scale. Also, there was experience to be gained in reconstructing sedimentary depositional environments from a geological analysis of the rock core. In addition, with this information, new answers for producibility and fracturability could be explored. GEOLOGICAL BACKGROUND STRATIGRAPHY The trend of the subsurface Jurassic (160 million years ago) extends from the Florida Panhandle around the Gulf Coast to northern Mexico, a distance of 1500 mi. See Figure 3. P. 35
Well logs are the foundation on which characterization of layered reservoirs is based. However, multi-well normalization of the well logs is necessary to reduce the probability of major errors and inconsistencies in the results of the log analysis. If not removed, these inconsistencies will cause failure in any attempt to integrate log analysis results with core, well test, and production data. This paper presents a comprehensive procedure for multiwell normalization of well logs. Use of this method will ensure that the well log data can be used effectively in reservoir characterization. The advantages of multi-well normalization are illustrated in three examples of integrated reservoir studies. Example 1 illustrates the multi-well normalization process using both histograms and M-N crossplots to verify the normalization. Example 2 from a 300 well reservoir study shows the use of multi-well dual-porosity crossplot with the histogram normalization. Example 3 introduces the benefits of multi-well normalization for permeability calculations from well-logs and the effect of removing the log errors in developing a relationship between the log response and permeability. This example also illustrates the integration between well-logs and core data. Introduction Practice in using well log analysis as a part of integrated reservoir studies has shown that for the results to be accurate, consistent and comparative well-to-well, the log data require corrections' with a process called multi-well normalization. This process ensures that each logging tool reads the correct values, i.e., that the density tool accurately records formation density, the neutron log accurately reflects hydrogen index, and so forth. Experience indicates that approximately 65 to 70 percent of gamma ray logs, 50 percent of density logs, 40 to 50 percent of neutron logs, and five to 10 percent of sonic logs require some normalization to correct for variances in field calibrations of the logging tools. The normalized well log data can be effectively integrated, correlated, and calibrated with core data. The resulting correlations can be extended vertically to include layers which were not cored and laterally from well-to-well across the study area. The difference in the scale of measurement of the two sets of data must be taken into account. The core data have a scale of few cubic inches, while the log data have a scale of a few cubic meters and well test data have a scale of a few acres. Table 1 shows that even among the log measurements there are different volumes of investigation for the different tools. Multi-Well Normalization Multi-well normalization is a key activity to ensure accurate and consistent results from a multi-well log analysis study. Normalization is an iterative process that uses three tools; histograms, crossplots, and depth-based logs. These tools may be applied in the rock layers being analyzed or in nearby layers. In a marine environment of deposition, the nearby or interbeded shales may be consistent enough over a large area for normalization purposes. For instance, the Bossier shale in East Texas can be used in the normalization process. In many basins, there are often enough very low porosity carbonates with sufficient areal extent to be useful in the normalization process. This is especially true in evaporate deposition cycles. When sandstone is abundant such as in the Travis Peak & Cotton Valley of the East Texas, Prairie du Chein of Michigan, Lorelle formation of Australia, the Miocene reservoirs of the Gulf of Suez in Egypt, and many others, the sandstone itself can be used in the normalization process. P. 139^
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