Extraction of oil and gas can cause reduction in pore pressure, occasionally resulting in subsequent compaction that forms a surface subsidence bowl, especially in shallow reservoirs. In the last 10 years, there has been over 10 feet of subsidence in parts of the Lost Hills oil field in California (Bruno et al.,1992). The surface subsidence at Lost Hills not only causes damage to surface facilities and wells, but also reactivates faults and reduces rock permeability. Subsidence makes reservoir optimization difficult. Hence, it is important to assess or predict the surface subsidence and the reasons for subsidence early in the life of an oil field to make an optimization plan. We use jointly the capacitance resistance model (CRM) (Alberoni et al., 2002 and Yousef, et al., 2006) that relies only on injection and production data, and the InSAR satellite imagery of surface subsidence. From CRM simulations, we estimate the connectivity between injectors and producers as well as general water flow directions from individual injectors. We then superimpose well connectivity and InSAR imagery to diagnose the reasons for the subsidence. Using new surface subsidence models, which are based on the continuity equation of CRM and rock mechanics, we are able to predict the average surface subsidence at Lost Hills from the injection and production rates. Our work shows that there was significant volumetric rock damage at Lost Hills and the well connectivity changed dramatically with time because of reservoir compaction and the rock damage. We conclude that for a soft, fragile and nearly- impermeable rock such as the diatomite, high injection rate weakens the rock and creates dynamic water flow tubes or ‘channels’ without providing good pressure support to the reservoir. These high permeability ‘channels’ re-circulate most of the injected water between the injectors and producers. Our CRM/InSAR approach is new and gives insights into the time-dependent and spatially variable fluid flow fields in a relatively shallow waterflood. Consequently, we may be able to suggest optimum water injection strategies to enhance oil production, while minimizing rock damage and surface subsidence. In addition, the proposed surface subsidence models are convenient and reliable to predict the average surface subsidence. / text

Reservoir characterization is very important in reservoir management to plan, monitor, predict and optimize oil production. Reservoir simulation is well-accepted in reservoir management but it requires many inputs, needs months to set up and complete a set of simulation runs, and contains large uncertainty in physical and geological properties. Therefore, simpler methods that provide quick results to complement or substitute reservoir simulation are important in decision making. Capacitance resistance model (CRM) is one of the methods. CRM is an input-output model derived from a continuity equation to quantify producer-injector connection strength during waterflood using solely production data. This work improves the CRM application method for waterflood and develops CRM theories and application methods for other recovery periods such as primary recovery and water-CO2 flood. A West Texas field test was carried out to validate CRM for a waterflood. The CRM fit was evaluated and used to optimize the oil production by changing injection rates. Through this first field experiment, a CRM application procedure was developed. With the CRM optimized injection schedule, the field gained 5372 bbls of additional oil production increase after one year. This research also quantitatively validates the CRM gain and time constant using synthetic fields and compares them to parameters of the streamline model, a complex model with similar purposes to the CRM. The CRM provides similar results as the streamline model with fewer inputs. The CRM was extended to primary recovery and water-CO2 flood. A new CRM equation – the integrated CRM (ICRM) - for primary recovery was developed and validated on many synthetic fields and an Oman field. The model can estimate dynamic pore volume, productivity index and average reservoir pressure that compare closely to simulated values and field knowledge. Additionally, the ability of CRM to quantify injector-producer connection strength and predict fluid production was examined on a synthetic water-CO2 flood field. A new oil production model to be used with CRM application in water-CO2 flood was developed and validated on synthetic data. The model predicts oil production from injection rate and relative permeability. CRM has successfully optimized waterflood on a West Texas field by reallocating the water from ineffective to effective injectors. New interpretations of the CRM parameters enable quantitative validation and integration of the CRM results with other methods. In primary recovery, the ICRM can estimate reservoir properties without requiring well testing which can cause loss of production. The CRM and the new oil production model can quickly characterize water-CO2 flood for short term production monitoring. / text

Significant quantities of hydrocarbon are bypassed during conventional waterfloods. This is the direct result of fluid channeling through high permeability zones within the reservoir. Conformance control offers a mean of increasing vertical and areal sweep efficiency, thus decreasing the amount of hydrocarbon bypassed. This, in turn, results in increased hydrocarbon production, decreased water cut, and field life extension. This thesis focuses on the use of polymer microgels as a relatively novel conformance control agent. Polymer-microgel-enhanced waterflooding tackles fluid channeling by “plugging” high permeability channels, or thief zones, and diverting trailing flooding fluid to adjacent poorly swept areas of the reservoir. The first major objective of this thesis was to provide an extensive literature survey on polymer microgel technology, which can serve as the go-to reference on this topic. Colloidal Dispersion Gels (CDGs), Preformed Particle Gels (PPGs), temperature-sensitive polymer microgels (Bright Water), and pH-sensitive polymer microgels are all discussed in detail, and an attempt is made to highlight the potential mechanisms by which they plug thief zones and improve oil recovery. This thesis then outlines the results of simulating numerous polymer microgel floods, ranging from experimental cases to field cases. Specifically, Colloidal Dispersion Gels (CDGs) were chosen for the simulations undergone. All simulations were run using UTGEL, a newly developed in-house simulator designed exclusively for the simulation of polymer, gel, and microgel floods. The simulations performed provide insight on the polymer microgel flooding process, and also served as a means of validating UTGEL’s polymer microgel (CDG) models. The development of the UTGEL simulator was important as it enables the optimization of polymer microgel floods for maximized hydrocarbon recovery efficiency. The results of a simulation study, using a synthetic field case, are also outlined. This sensitivity study provides additional insight on optimal operational conditions for polymer microgel technology. More specifically, this study aimed to investigate the effectiveness of microgel flooding treatments in layered reservoirs of varying permeability contrasts, vertical-to-horizontal permeability ratios, and under a variety of different injection concentrations. / text

This dissertation focuses on interpreting the spatial variations of seismic amplitude data as a function of rock properties for the Haynesville Shale. To achieve this goal, I investigate the relationships between the rock properties and elastic properties, and calibrate rock-physics models by constraining both P- and S-wave velocities from well log data. I build a workflow to estimate the rock properties along with uncertainties from the P- and S-wave information. I correlate the estimated rock properties with the seismic amplitude data quantitatively. The rock properties, such as porosity, pore shape and composition, provide very useful information in determining locations with relatively high porosities and large fractions of brittle components favorable for hydraulic fracturing. Here the brittle components will have the fractures remain opened for longer time than the other components. Porosity helps to determine gas capacity and the estimated ultimate recovery (EUR); composition contributes to understand the brittle/ductile strength of shales, and pore shape provides additional information to determine the brittle/ductile strength of the shale. I use effective medium models to constrain P- and S-wave information. The rock-physics model includes an isotropic and an anisotropic effective medium model. The isotropic effective medium model provides a porous rock matrix with multiple mineral phases and pores with different aspect ratios. The anisotropic effective medium model provides frequency- and pore-pressure-dependent anisotropy. I estimate the rock properties with uncertainties using grid searching, conditioned by the calibrated rock-physics models. At well locations, I use the sonic log as input in the rock-physics models. At areas away from the well locations, I use the prestack seismic inverted P- and S-impedances as input in the rock-physics models. The estimated rock properties are correlated with the seismic amplitude data and help to interpret the spatial variations observed from seismic data. I check the accuracy of the estimated rock properties by comparing the elastic properties from seismic inversion and the ones derived from estimated rock properties. Furthermore, I link the estimated rock properties to the microstructure images and interpret the modeling results using observations from microstructure images. The characterization contributes to understand what causes the seismic amplitude variations for the Haynesville Shale. The same seismic reservoir characterization procedure could be applied to other unconventional gas shales. / text

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A new three-angle energy-dispersive (ED) diffractometer has been successfully commissioned on station 16.4 SRS, Daresbury, England. The diffractometer facilitates the simultaneous collection of three spectra at three Bragg scattering angles. This enables the sampling of a far greater range of reciprocal space as compared to conventional single-angle diffractometers. Additionally the arrangement allows changes in sample density to be monitored. A protocol has been developed to align the diffractometer such that the origins of the diffracting volume are coincident on the diffractometer axis. Spectra obtained from the diffractometer were improved by the construction and placement of shielding. Experimental determination of components of the resolution function show that the resolution is close to the instrumental limit. The flux distribution of station 16.4 was determined experimentally. A novel whole pattern method has been developed for the quantitative analysis of synchrotron ED diffraction data. The method, which accounts for the differential absorption across the ED spectrum, was developed using spectra collected from a set of test binary phase mixtures and pure phases. Parameters relating to the proposed models were determined using linear and non-linear least-squares methods. Although the final model is the most physically complete it does not take account of certain non-diffraction derived events which appear as counts within the test spectra. A novel application of synchrotron ED diffraction, energy-dispersive diffraction tomography (EDD-T), is described. The method facilitates the non-destructive examination of the interior of crystalline and semi-crystalline objects. The resolution and limitations of this technique have been demonstrated using test objects. The method has been used to map the phase distributions of a variety of materials in a range of different samples. Quantitative EDD-T was used to determine the invasion of calcite into simulated oil-reservoir rocks.

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Mollusk shells from Peruvian archaeological middens provide brief (< 5 yr per shell) records of past marine conditions. Marine radiocarbon age, R, is recorded in shell carbonate at the time of precipitation. R varies with changes in upwelling: when radiocarbon-depleted sub-thermocline water wells up, R is large; increased contribution from radiocarbon-enriched surface water (due to seasonal cycles or an El Niño event) reduces R. Are molluscan records of R a useful proxy for Peruvian upwelling? If so, does R from archaeological shells reveal mid-Holocene upwelling changes that constrain the Holocene history of El Niño-Southern Oscillation (ENSO)? Profiles of R along ontogeny from early 20th century Argopecten purpuratus (bay scallop) shells and mid-Holocene A. purpuratus, Mesodesma donacium (surf clam), and Trachycardium procerum (cockle) shells from eight coastal Peru locations show that R varies by up to 530 ± 200 ¹⁴C yr within individual shells. El Niño events are easily detectable in post-1950s shell carbonate due to increased radiocarbon contrast between sub- and super-thermocline water from “bomb carbon,” but R differences between El Niño and La Niña shells from the early 20th century are subtle. Decreasing precision in older shells due to ¹⁴C decay makes detecting El Niño events in the archaeological past using radiocarbon very difficult. Because of intrashell radiocarbon variation, caution is prudent when using marine material for chronometry in variable upwelling environments. Based on modeling, mollusks that grow seasonally rather than year-round can skew long-term average (> 1 yr) R reconstructions by nearly 200 ¹⁴C yr toward R of the preferred growth season. Coldloving M. donacium, for example, records older marine reservoir ages on average than A. purpuratus in the same water, because A. purpuratus grows in both warm and cold conditions. Comparisons of R between species with opposite seasonal growth habits can compound this effect. Because of intrashell R variation, seasonal growth biases, and measurement uncertainties, a change in R due to past ENSO changes would have to be hundreds of ¹⁴C yr or greater to be identifiable. Thus far, clear evidence for such a Holocene change in R has not been seen.