Development of source-rock resources relies on the rigorous knowledge of their petrophysical properties such as porosity, permeability, and hydrocarbon saturation. In parallel, a concise description of the wettability and pore structures is commended. This paper presents a detailed Nuclear Magnetic Resonance (NMR) T2 study of the wetting characteristics and pore structure in organic-rich source rocks from different locations including the Eagle Ford formation. Although these rocks are highly laminated and calcite dominated, our studies indicated that they have distinct different pore structure and connectivity, and differ in how TOC is dispersed within the rock fabric. We believe that the entailed findings could influence our thinking on how best to produce these shales, wellbore stability, drilling fluid selection and other asset development actions.
Source-rock samples with varied amount of total organic content (TOC) were drilled perpendicular or parallel to the laminations. The samples were cut into twin plugs which were sequentially saturated by spontaneous imbibition of 5% KCl brine and diesel (oil). The NMR T2 measurements were used to determine the fluid imbibition rate and amount, as well as the porosity associated with organic and inorganic components of the source rocks. The fracture apertures were obtained via an application of characteristic T2 cutoff times to the NMR T2 distributions. The mineral elements, phases and TOC of the rocks were measured using X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and HAWK pyrolysis, respectively.
The prevalence of surface relaxation on the NMR dynamics was prominent as the transverse relaxation took place at time scales (T2 ≤ 100 ms) much shorter than their bulk values. The overall wettability of the samples showed a mixed character as the brine and the oil had been intimately imbibed. Nevertheless, the details of the wetting behavior of the Eagle ford samples and the other samples were different. For instance, Eagle Ford samples imbibed larger volumes of brine and faster than oil, on the contrary the other samples imbibed larger volumes of oil and faster than brine.
The apparent preference of oil on the other samples is attributed to their high TOC compared to the Eagle Ford samples. Upon imbibition in these samples, brine is observed to flow along the clay rich bedding planes. In fact, the interaction between brine and clay is identified to be the potential driver of the rock stability problems especially near the wellbore; however it is constrained by the type of residing clays. The discrepancies in the wetting traits are magnified by the presence of fractures which enhanced the network connectivity of both hydrophobic and hydrophilic pores or even across them. Furthermore, the fractures allowed the fluids to surpass the vertical bedding planes and thus accelerating the fluid distribution processes inside the pore space. The fracture apertures were found to range from 1 μm to 15 μm which are typical values for source rocks (
In Kuwait, the traditional approach to Field Development has been to drill wells, whether Vertical or Horizontal, Single or Dual, with completions dedicated to either Production or Injection. However, as increasingly more wells are being drilled to develop the stacked reservoirs, surface infrastructure is growing in complexity with regard to Production Flowline routing, Gathering Facility location, Satellite Manifold placement, Water Injection distribution lines routing, and access road construction. Also, since the reservoir stack is a combination of areally extensive Carbonates overlying shale & channel sand sequences, optimum surface locations of Injectors for one reservoir is now increasingly conflicting with the optimum surface locations for the Producer of another reservoir.
The North Kuwait team presented options that could reduce the requirement for excessive wellbores for both new Producers and Injectors. One of which is the utilization of a single wellbore to both Produce Oil from one reservoir and Inject Water into another reservoir simultaneously. This novel approach utilized the most popular Dual Completion equipment, but rather than produce or inject concurrently from separate reservoirs or layers, production & injection are achieved simultaneously through either tubing string. Tubing movement calculations were made to ensure that the resultant axial tubing forces exerted by simultaneously injecting cold water and producing hot reservoir fluid would not cause the Dual packer to prematurely unset.
This unique completion has several advantages which include the production acceleration from an adjacent reservoir/layer that would have been postponed for the life of the Injector and the elimination of the drilling of a new producer to access the oil from an adjacent reservoir/layer to the target injection zone. Additionally, the elimination of the drilling of an Injector well if its optimum subsurface location is close to, or coincides with, an existing Producer from an adjacent layer, and the reduction in access road construction and location preparation costs. This strategy will significantly reduce Unit Development Costs while concurrently ramping up production levels. With simple conversion workovers, rather than drilling new wells, Oil Production potential that is presently unexploited in dedicated Injector wells can immediately be realized. Pressure support Injection can be initiated as soon as distribution injection lines are made available via similar conversion workovers.
In mature oil fields, water, steam, natural gas, and carbon dioxide are purposely injected into a reservoir to increase pore pressure on the oil, to lower the viscosity of heavy oil, and, ultimately, to increase the oil recovery factor. The placement of oil, water, and gas within the reservoir is highly dynamic and not easily predicted. Therefore, reservoir monitoring is key to improving sweep efficiency and oil recovery.
Density is an important physical property for inferring oil, water, and gas saturation in a rock. Due to the density differences of oil, water, and gas, the saturation variation of each phase will have a direct impact on the measured gravity fields. The conventional well logging tool, gamma-gamma density, has a maximum depth of investigation (DOI) of 6 to 8in in open hole and greatly reduced accuracy in cased hole. A gravimeter, in contrast, yields a density measurement with inherently large DOI, where the DOI is determined by the vertical separation between pairs of differenced measurements of the acceleration due to gravity. For example, the DOI resulting from a pair of measurements separated by 3m will be approximately 4.5m.
In this paper, we have conducted extensive simulations of using borehole gravity fields to monitor water flooding from injectors. In one scenario, we considered fracture systems within the reservoir typically identified by seismic methods; however, their impact on water flooding is not fully understood. Borehole imaging and production logging measurements clearly identify where fractures are along the borehole. However, due to their limited DOI, there is no clear picture about fractures farther from the borehole. Because the fractures are most probably filled with water and rock other than formation rock, which have a density different from that of the surrounding formation matrix, the borehole gravity field with its large DOI could provide useful information. To understand the response and the sensitivity of the borehole gravity measurements, we constructed a reservoir model with fractures of different sizes and locations within the modeled volume. From the lithology and fluid properties, density information was computed and propagated in the model. A vertical well was used as the survey location of the borehole gravity measurements. Both gravity and differential fields were calculated. The simulations were designed to address the following questions: Does the borehole gravity measurement have enough sensitivity to detect fractures within a reservoir? How far away from a borehole can fractures be accurately identified?
Does the borehole gravity measurement have enough sensitivity to detect fractures within a reservoir?
How far away from a borehole can fractures be accurately identified?
This paper will present our simulation results and discuss their implication for reservoir fluid-front monitoring. Although borehole gravity measurements have not been used in reservoir monitoring, this study's results demonstrate the advantage of data acquisition with large DOI, which provides a huge operational benefit and cost-effective measurements to manage oil fields.
Gangway equipped: offshore support vessels, intervention vessels, construction vessels, and other monohull vessels, capable of providing gangway access to offshore facilities in exposed sea areas has great potential. It is playing an evolving important role in making new marginal yield field development economical, reducing exposure to risk, and extending the life of the existing oil and gas infrastructure. Otherwise known as Walk to Work (W2W), this marine manning approach for offshore facilities can be used on a regular, fixed term, ad-hoc or exceptional circumstance basis. It is capable of providing significant benefits over existing provisions including: improved safety, increased workforce productivity, greater manning flexibility, and reduced lifecycle costs. The W2W vessel can range from relatively small, fast workboats, to large semi-submersible'flotels' stationed alongside fixed platforms. Within this range, it is the mono-hull vessel where there is the greatest opportunity for the oil and gas industry to realise significant (currently unexploited) gain. Depending on the capability of the chosen vessel, a W2W solution may offer: gangway transfers, hotel, hospital, helicopter, rescue and recovery, subsea and splash zone inspection, cargo, crane, fabrication and other facilities.
The process of mining causes changes in the seismic velocity of the rocks in the vicinity of the openings. Two effects are present: First, increased stress in the rockmass results in an increase in seismic velocity. Second, regions where the rock is highly fractured show lower seismic velocity and higher attenuation. Mapping the seismic velocity distribution and changes in velocity caused by mining could have two immediate benefits: mining-induced seismic events could be more accurately located, allowing their use in assessment of rockburst hazard; and the zones of high stress and fracture could potentially be directly imaged. A geophone array installed on the surface above a longwall coal mine was used to record seismic signals from the shearer as it cut coal. Major differences in velocity were seen for regions in front of the mining face compared to the highly fractured and caved zones behind the face. In order to test the viability of imaging this caved zone behind the face, a sledgehammer source was used in an underground roadway to augment the data from the shearer, and refracted arrivals were generated using surface sources. Images produced from this data repeatedly show, not only a low-velocity caved zone behind the face, but also a high-velocity region in front of the face which could be caused by increased stress in this region. The conclusion is that seismic changes caused by mining are large enough to be detected and imaged.
Hornbach, Matthew J. (The University of The West Indies) | Brown, Lyndon (The University of Texas) | Mann, Paul (The University of The West Indies) | Frohlich1and, Cliff (The University of The West Indies) | Ellins1, Kathy (The University of The West Indies)
Kingston, Jamaica, the capital of the Caribbean island nation of Jamaica is prone to infrequent but devastating earthquakes and tsunamis, yet the locations of the faults responsible for generating these geohazards are poorly known. During the past few hundred years, at least two earthquakes have triggered severe liquefaction across Kingston and generated tsunami within the Harbor, resulting in significant destruction. The goal of our study is to (1) determine the location of faults in Kingston Harbour, (2) assess whether these faults are active, (3) determine whether harbor faults triggered local tsunami reported during the 1692 and 1907 Earthquakes, and (4) from this, constrain the risk of future geohazards across the region. Here, we focus our analysis on recent results from our January 2011 chirp seismic imaging survey of Kingston Harbour. These data reveal a complex fault system extending across the harbor and evidence for multiple slide and liquefaction events. Using sea-level curves as a means of constraining age, we suggest these faults are active. Our study suggest east Kingston where the Cement Factory, twp power plants, a fuel-depot, Highway A4—the only east-west thoroughfare extending east of Kingston, The Norman Manley Airport, and the town of Port Royal are all prone to significant damage during the next earthquake in this region.
Gasperikova, Erika (Lawrence Berkeley National Laboratory) | Smith, J.T. (Lawrence Berkeley National Laboratory) | Kappler, K.N. (Lawrence Berkeley National Laboratory) | Morrison, H.F. (Lawrence Berkeley National Laboratory) | Becker, A. (Lawrence Berkeley National Laboratory)
Because hand-held systems have the advantage of being lightweight, compact, portable, and deployable under most site conditions, they are particularly useful in areas of dense vegetation or challenging terrain. In heavily wooded areas or areas with steep or uneven terrain, hand-held sensors may be the only suitable device for unexploded ordnance (UXO) detection and discrimination because it can be carried through spaces that the operator could walk through or at least approach. Based on these considerations, we designed and built a sensor package in a shape of a 14-in (0.35 m) cube. This time-domain electromagnetic hand-held prototype incorporates the key features of the cart-mounted system — (a) three orthogonal transmitters and ten pairs of receivers, and (b) difference or gradient measurements that significantly reduce the ambient and motion noise, and greatly enhance the sensitivity to the gradients of the target. Electromagnetic induction data transformed into time dependent object intrinsic polarizabilities allow discrimination of UXO from false targets (scrap metal). A near-intact UXO displays a single major polarizability coincident with the long axis of the object and two equal smaller transverse polarizabilities, whereas metal scraps have distinct polarizability signatures that rarely mimic those of elongated symmetrical bodies. Our prototype results have demonstrated that the same discrimination capabilities afforded by the cart-mounted system are available in the hand-held unit albeit with a slightly reduced depth of detection. The hand-held UXO discriminator is able to discriminate small (20 mm) objects at a depth of 0.45 m and large (105 and 155 mm) objects at the depth of 0.85 m. Large objects are detected down to 1.15 m.
Microseismic event locations are increasingly used as input parameters for additional calculations, e.g. stimulated reservoir volume (SRV), moment tensor inversions. Uncertainties in the event locations often have a direct effect on the derived parameters and therefore it is important to quantify the location uncertainty. Although companies generally report location uncertainties in form of error bars, often along Cartesian coordinates, the calculation of these error bars and their interpretation is not standardized and sometimes obscure. By assigning each point in the localization grid a probability for the event location based on the available input data it is possible to use input from very different sources, e.g. traveltime residuals, hodogram analysis, velocity model uncertainties, and combine them in a probability grid. The distribution of the overall probability can then be used to define the uncertainty space based on the desired level of accuracy, e.g. the 95% confidence uncertainty space will be larger than the 90% confidence space. This method has the advantage that very different types of uncertainty, e.g. sensor position, can be included in the calculation and that an interpretation of the uncertainty space in terms of confidence is possible. The derived uncertainty space clearly represents the space where the event is with 90%, 95% or any other degree of probability.
Nolan, Jeffery J. (US Army Engineer Research & Development Center) | Sloan, Steven D. (US Army Engineer Research & Development Center) | Broadfoot, Seth W. (US Army Engineer Research & Development Center) | McKenna, Jason R. (US Army Engineer Research & Development Center) | Metheny, Owen M. (US Army Engineer Research & Development Center)
Subsurface voids may manifest themselves as natural or anthropogenic dissolution features, illegal cross-border tunnels, or abandoned mines. Detection of these voids using geophysical methods has often proven difficult due to multiple factors including depth-to-diameter ratio, lack of resolution, non-uniqueness, etc. Experiments were conducted at a test site with a known subsurface void to determine the capability of multiple near-surface seismic methods as applied to void detection. In this study, refraction tomography and multichannel analysis of surface wave methods successfully identified a man-made void approximately three meters deep. Results of these experiments correlated well with the expected results, exhibiting decreased velocity, the absence of seismic ray coverage, and a high shear-wave velocity halo above the void.
The Common-Reflection-Surface (CRS) method may improve seismic processing beyond imaging, e.g. in an enhanced Amplitude Versus Offset (AVO) analysis. Various applications have shown that the more realistic subsurface assumptions, and the increased fold of the CRS imaging allow to extend AVO analysis into noise zones and to deep targets with low signal quality. Extreme fluctuations of AVO parameters are removed, and AVO anomalies are enhanced. The CRS method assumes subsurface reflector elements with dip and curvature, which implies large-fold stacking surfaces extending both across offset, and across neighboring CMP locations. The extension across neighboring CMPs defines a CRS gather at the central CMP location, comprising data from a multitude of traces. The CRS moveout correction compensates for the local dip across these neighboring CMPs, thus contrasting to conventional AVO super-gathers based on NMO correction that collect dipping events horizontally at varying phase. The presented case studies show that CRS-AVO attribute stacks are produced with a much higher signal-to-noise ratio from CRS gathers than from CMP gathers in conventional AVO. The CRS-AVO attribute sections clearly distinguish anomalies at known or expected gas-bearing reservoirs. Cross-plots of CRS-AVO attributes show a better separation of anomalous zones which may be classified in order to identify top and base of hydrocarbon deposits.