One major drawback in the implementation of CO2/surfactant enhanced oil recovery is the high cost of the surfactant volume needed and the extrapolated amount of surfactant required for use in the field. Therefore, there exists a need for a methodology to evaluate the most economic surfactant volume that will lead to optimum oil production.
This paper presents the results of laboratory experiments that were designed to study the performance of foam injection and to obtain information on the parameters that will be utilized in a future modeling study to determine the minimum but most effective volume of surfactant needed for optimum foam generation and hence oil recovery in a porous medium. The effect of reservoir pressure and surfactant concentration is studied.
Carbon dioxide and surfactant solution were co-injected into Berea sandstone core that was saturated with brine and oil after a waterflood process. Some of the values of parameters utilized in the experiments include surfactant concentrations of 0.1 wt % and 0.5 wt %, average back pressure of 2350 psi and total flowrate of 0.4 cm3/min, with CO2 injected at 0.3 cm3/min and surfactant concentration at 0.1 cm3/min, which results in a volumetric flow ratio of 3:1 and foam quality of 75%.
Results show that at a higher surfactant concentration, more oil was recovered, and a steady increase in pressure difference was observed. This indicates that foam was formed, which was also seen at the production end of the system. The foam created during the experiments with the 0.1 wt % surfactant concentration, on visual inspection, appeared to be weaker than that formed in the case of the 0.5 wt % concentration.
Remote sensing of fractures with elastic waves is important in fields ranging from seismology to non-destructive testing. While previous analytic descriptions of scattering mostly concern very large or very small fractures (compared to the dominant wavelength), we present an analytic solution for the scattering of elastic waves from a fracture of arbitrary size. Based on the linear-slip model for a fracture, we derive the scattered amplitude in the frequency domain under the Born approximation for all combinations of incident and scattered wave modes. Our analytic results match laser-based ultrasonic laboratory measurements of a single fracture in clear plastic, allowing us to quantify the compliance of a fracture.
Barnes, Simon (PGS) | van Borselen, Roald (PGS) | Salazar, Humberto (Pemex Exploration and Production) | Vàzquez, Alfredo (Pemex Exploration and Production) | Ronzón, Israel (Pemex Exploration and Production) | Martinez, Ruben (PGS)
A processing strategy for the 3D prediction and subsequent elimination of long period surface-related multiples (SRME) contaminating a 3D sparse non-orthogonal land seismic data is presented. A comparison is made between 1D and 3D multiple prediction using the Surface-related Multiple Elimination (SRME) method, showing that significant improvements can be obtained by taking into account the full 3D complexity of the subsurface. Multidimensional Fourier regularization has been proven to be a critical component of the pre-conditioning of the data applied prior to the multiple prediction and subtraction.
A new method has been developed to derive time strain volumes from multiple time shift volumes. A workflow has been proposed to merge time strain volumes with 4D difference seismic volumes to derive Broadband Time Lapse volume (BBT). The workflow is simple and cost efficient for maximizing the 4D information.
Wavefront construction is a method used for fast seismic ray tracing. An essential process in the method is the interpolation of traveltimes from an irregular grid to a regular grid. Usually, this interpolation is realized by using bilinear interpolation. However, bilinear interpolation cannot give continuous derivatives across the grid element used for realizing interpolation. Therefore, it is not adequate for ray tracing in complex media with certain smoothness, because for computing rays traveltime derivatives should be continuous everywhere in the smoothed model. To have an interpolation scheme that meets the requirements for solving ray tracing system numerically, we introduce a two-dimensional cubic convolution interpolation. It is found that the two-dimensional cubic convolution interpolation is efficient and accurate in comparison to bilinear interpolation. Also, it is found that the difference between the ray families respectively computed by the two-dimensional cubic convolution interpolation and by bilinear interpolation is large when the velocity change in the model used is strong. This leads to the conclusion that for obtaining correct ray trajectories in the complex velocity model, an interpolation formula with a smoothness order higher than that of bilinear interpolation formula is necessary.
Fractures and cracks in carbonate rock cause secondary porosity, which affects fluid behavior and production of oil and gas. Therefore, evaluation of fracture properties is crucial to optimize oil and gas production. To this end, we investigated representative seismic response in fracture zone, seismic anisotropy and scattering energy, by physical modeling. We found that application of conventional processing under an assumption of isotropy to anisotropic dataset from physical and numerical modeling experiments, resulted in inaccurate imaging of the reflection interface. Furthermore, scattered energy was found to be most incoherent and irregular when the receiver of the model moved in the direction normal to the fracture strike.
Injection and migration of CO
Variable-depth streamer acquisition is becoming a key technique for providing wide bandwidth seismic data. Varying the receiver depth creates wide receiver ghost diversity and produces a spectacular increase in the frequency bandwidth. However, compared to conventional data, this variable-depth streamer data implies a major challenge in processing: how to deal with various receiver ghosts. The ghosts have to be preserved up to the deghosting step. Here we present the implication for the following de-multiple methods: Shallow-Water De-multiple, Tau-P deconvolution and Surface-related multiples elimination in deep and shallow water environments.
A zero offset VSP survey was acquired over a thick carbonate interval. The objectives of the repeat survey were to assess repeatability of the measurement, robustness of the time lapse VSP processing mainly to account for time lapse noise and quantification of the time lapse signal in the reservoir due replacement of water by gas caused by gas injection that occurred between the baseline and repeat surveys.
A long side of the two VSP's, an array sonic (SDT) and the sonic scanner tools were run. The SDT was run to recover the monopole compresssional and shear waves, while sonic scanner to acquire both the dipole and monopole shear and compressional.
Data processing was focused on isolating the time lapse signal in the reservoir section by comparing the baseline and repeat VSP surveys and sonic logs. Both the baseline and repeat surveys were processed with identical parameters to ensure that the datasets are comparable at every processing step. The processed data shows a good degree of repeatability, and deterministic deconvolution as expected was enough to take care of source wavelet variations between the two surveys.
The time lapse VSP and sonic logs were run in carbonate reservoirs where gas is being injected to assess the effectiveness of recovering more oil as part of Enhanced Oil Recovery (EOR). The current recovery mechanism in the reservoirs is to inject water to enhance pressure support. The gas pilot objective is to increase the recovery factor to recover more oil and enhance productivity.
Rocco, Guillermo (Petroleum Development of Oman) | Adawi, Rashid (PDO) | Al-Busaidi, Khalfan Hamoud (PDO) | Rodriguez, Francisco Alberto (Petroleum Development of Oman) | Al-Busaidi, Said (Petroleum Development of Oman) | Al Kindy, Fahad (Petroleum Development of Oman) | Al Maamari, Abdullah (Petroleum Development of Oman) | Kiyaschenko, Denis (Shell International E&P) | Mehta, Kurang (Shell International E&P) | Lopez, Jorge L. (Shell Intl E&P Co) | Zwaan, Marcel (Shell Intl E&P Co) | De Zwart, Albert Hendrik (Shell Intl E&P Co)
A steam flood re-development of a mature field in the South of Oman is well underway with the first pattern of steam injection active since late 2008. The areal surveillance programme designed by a joint effort between Petroleum Development Oman (PDO) and Shell International Exploration and Production (SIEP) includes the simultaneous recording of a variety of seismic methods of different resolution. The main purpose of the time-lapse work is to monitor the steam conformance and sweep efficiency as the steam is injected in this heavy oil reservoir over 1,000 m below surface. Key aspects of the data acquisition campaigns, state-of-the-art processing and timelapse interpretation will be discussed. The ultimate objective of the programme is to evaluate the effectiveness of the techniques used in order to select the most appropriate and economically viable reservoir surveillance tools for full field deployment.