Rashaid, M. (KOC) | Al-Ibrahim, M. (KOC) | Van Steene, M (Schlumberger) | Ayyad, H (Schlumberger) | Friha, A. (Schlumberger) | Liang, L. (Schlumberger) | Cig, K. (Schlumberger) | Ayan, C. (Schlumberger) | Habashy, T. (Schlumberger) | Cherian, J. (Schlumberger)
Relative permeability and capillary pressure are essential information for reservoir modeling, as they impact production optimization and reservoir management. Obtaining this data from special core analysis can take a significant amount of time. Furthermore, it can be challenging to guarantee that the core is restored to its original reservoir wettability state. Additional challenges include cost, scale, and the presence of contamination or alteration. Other emerging techniques, like digital rock, face similar issues. A new workflow has been designed to address those challenges and complement the traditional core analysis offering, by obtaining relative permeability and capillary pressure in-situ from wireline formation tester (WFT) and open hole logging measurements.
In this workflow, a near-wellbore reservoir model is built to simulate the mud-filtrate invasion. This reservoir model, combined with an electromagnetic model, simulates resistivity logs, and subsequent pressure transient and mud-filtrate cleanup processes induced by WFT formation testing. Petrophysical log analysis, using array resistivity, nuclear magnetic resonance, and dielectric measurements, is performed to provide prior information for the model initialization. Vertical interference testing from WFT at the same depth provides permeability anisotropy. An optimization engine is employed to update the selected reservoir model parameters until the simulated resistivity logs, pressure transient, and water-cut data match their measured counterparts. Relative permeability and capillary pressure are estimated together with other parameters including mud-filtrate invasion volume and permeability. Both stochastic and deterministic methods are used for the inversion. The deterministic method is cost-effective if a good initial model can be obtained, while the stochastic method is able to find the minimization function's global minimum but needs high computational effort.
This workflow was applied to one well in the Ahmadi field in Kuwait, targeting an inter-tidal deposit. In-situ relative permeability and capillary pressure curves were obtained by the deterministic and stochastic methods using formation testing data and petrophysical logs acquired over the interval. The results are consistent between the two methods and representat the effective formation properties in the surveyed interval.
This case study demonstrates that it is possible to obtain in-situ relative permeability and capillary pressure data from commonly acquired wireline measurements. The delay in obtaining the relative permeability and capillary pressure data is significantly reduced compared to special core and digital core analysis techniques. Since the measurement is performed downhole, it doesn't suffer from the doubts that surround the core samples restoration process to original reservoir conditions. The formation volume investigated by this survey, in the order of several feet, represents the formation macroscopic properties, thus bridging the gap between core scale and reservoir scale.
This paper presents a significant methodology advancement that addresses one of the industry's most challenging problems: the accurate prediction of detailed local stresses in unbonded flexible risers. Flexible risers exhibit highly nonlinear dynamic behavior due to the stick/slip interaction between the pipe wall layers in compliant systems that undergo large three-dimensional translations/rotations. Practical, accurate prediction of critical flexible pipe component responses requires an efficient method capable of incorporating detailed flexible pipe models into a global nonlinear dynamic analysis. Current industry practice is a two-step global/local approach involving a global nonlinear analysis with 1D centerline models, which may include bending hysteresis effects, followed by local analysis of a detailed model segment to the global results to predict critical response items such as armour wire stresses.
A Nonlinear Dynamic Substructuring (NDS) framework is developed that expands the classical methods of dynamic substructuring and component-mode synthesis to geometrically and locally nonlinear problems. This evolution/integration of capabilities enables the computationally efficient inclusion of detailed flexible pipe models into, and recovery of detailed response/stress time-histories directly from, the global nonlinear analysis itself. The NDS methodology is benchmarked against published work involving the large deformations static and dynamic global analysis of a flexible riser. The full potential of the method is then demonstrated by efficiently incorporating 3D detailed flexible pipe substructure models, with bending hysteresis, into a global system nonlinear analysis and recovering stress time-histories in tensile armour layers.
The accurate prediction of local stresses in flexible risers has been an industry objective for some time. Flexible pipe has a complex structure composed of multiple interacting pipe wall layers (Figure 1). The stick/slip friction hysteretic behavior of these layers is directly coupled to the global large displacements of the overall compliant system resulting in a highly nonlinear problem. A common approach for analyzing flexible risers is to conduct the global analysis with standard line elements utilizing the flexible pipe's unpressurized linear bending stiffness.
Evolution and wide-spreading of downhole monitoring systems has increased a lot over the last few years. Particularly downhole temperature data has been recognized as an important input for real-time production optimization. Whereas distributed temperature analysis and interpretation are the only methods used now, temperature evolution with time offers an excellent new source of information not yet fully understood. Simulation and analysis of temperature transients in wells are therefore a promising research area at the initial stage of development.
Near wellbore multiphase flow simulation considering heat transfer is not a simple task. There are aspects such as well-reservoir mutual influence where transient analysis needs to be considered. Neglecting thermal effects and completion design will result in inaccuracies of the physical phenomena representation.
This paper describes a non-isothermal dynamic well-reservoir simulator taking into account the presence of flow control valves in the wellbore. A fully coupled approach was used to solve the problem. The proposed model studied is two dimensional for the reservoir and one dimensional for the well. The reservoir is considered homogeneous, anisotropic and two-phase (oil/water or gas/liquid) saturated with the initial pressure above the bubble point. The well is vertical and the multiphase drift-flux model considering the radial influx is used to describe the flow in the wellbore.
Case studies for three-zone intelligent wells are analyzed from transient temperature profiles generated by the simulator. A single phase is used as a base case for the two-phase case. This paper shows that temperature transients from a step-change in production rate are able to provide full well-test equivalent information about each production zone. A downhole flow control valve step-change is also analyzed as a feasibility study of a well test without zonal shut-in. Restrictions of the simulator are presented and discussed for an appropriate use of the results.
Several researchers have published results showing the need of well-reservoir coupled simulation. Vicente showed in his isothermal model that the traditional approach of decoupling wellbore flow from reservoir flow in horizontal wells do not capture the interaction between them at early times (Vicente, Sarica et al. 2001). Grubets showed that the impact of completion design in the long-term well performance is not correctly achieved without two tier coupling between well and reservoir (Grubert, Wan et al. 2009). Alberts analyzed the dynamic behaviour in the well and reservoir identifying the time and space scales at which the well-reservoir coupling becomes important (Alberts, Belfroid et al. 2007). In Fig. 1 a time-space map from this work was reproduced in order to show the spatial and temporal relationship among common production processes. It is possible, for example, to see that well clean-up and reservoir transients have strong coupling and then should not be analysed separately (coincide completely). This simple idea can illustrate when one should consider well-reservoir coupling.
Multilayer reservoir well testing models have been developed and used successfully during the past two decades. The advances in downhole monitoring systems in recent years have motivated new testing and analysis techniques. Using transient temperature and pressure Sui developed a numerical simulator for qualitative analysis of changes in permeability and skin-factor in a multilayered vertical well (Sui, Zhu et al. 2008). They indicated that trasient temperature can be more informative than pressure due to its sensitivity to damage radius and permeability. Duru has found out that properties such as porosity and saturation could be estimated in an inverse problem from pressure and temperature transient analysis which are not available from conventional pressure transient analysis tools (Duru and Horne 2010). Valiullin highlighted the importance of Temperature Transient Analysis (TTA) especially when the barothermal effect (transient fluid compression/expansion at early times) takes place for well test analysis (Valiullin, Ramazanov et al. 2009).
We present a new technique for inverting 4D seismic data constrained by dynamics and geology. The inversion is first performed at well positions where all the constraints are set and afterwards extended to the full 3D dataset. The geological and dynamical constraints are set in the model definition i.e. a layered description of the geology (with permeable and non permeable layers) which may be different at each well. This information is then propagated concurrently from each well to the whole dataset. The way the inversion is posed prevents from side lobes effect and enables to discriminate density and velocity effects (P in the case of post-stack data and P&S in the case of prestack). The more reliable information is the P velocity since it affects both reflectivity and travel time.
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.
Refracted waves propagate along high-velocity layers and are highly sensitive to the changes within the layers of propagation. This property of refractions can be used for time-lapse monitoring, especially when the reservoir or its underlying layer is a high velocity zone (Hansteen, et al., 2010), e.g., carbonate formation. Application of the virtual source method (VSM) to refractions become useful when the overburden is complex and forms an obstacle for seismic imaging and monitoring. When VSM is applied to refracted arrivals, we generate a spurious event known as a virtual refraction (VR). Here we apply the concept of VR to a complex 3D synthetic dataset inspired by a typical field in the Middle East to show that the spurious arrival may be used to build time-lapse tomography images of reservoir anomaly zones.
The nearly perfectly matched layer (NPML) as a novel perfectly matched layer has been proven to be an excellent absorbing boundary condition to suppress the artificial reflection waves from the boundaries of truncated model. Here, NPML technique is applied to the first-order velocity-stress poroelastic wave equations. To test the absorbing performance of NPML, I provide the numerical comparison between NPML and convolutional perfectly matched layer (CPML) which is considered as one of the best boundary conditions.
Seismic wave illumination analysis provides the seismic wave energy and other information at the scattering point on a target layer, so it can be used to analyze imaging shadow and acquisition footprint, optimize acquisition geometry design and improve the imaging quality of prestack depth migration. However, the seismic illumination analysis based on either one-way or two-way wave equation is time-consuming. Therefore, this analysis is not widely used in practice. In order to improve the computational efficiency of seismic illumination without losing wave field characteristics, a new illumination analysis method which employs Gaussian beams to calculate seismic wave field is presented in this paper. Numerical examples indicate that the Gaussian-beam-based seismic illumination is a highly efficient tool to evaluate the effects of the designed seismic geometry.
Sil, Samik (ConocoPhillips Company) | Davidson, Michael (ConocoPhillips Company) | Zhou, Changxi (ConocoPhillips Company) | Olson, Robert (ConocoPhillips Company) | Swan, Herbert (ConocoPhillips Company) | Howell, Jack (ConocoPhillips Company) | Chiu, Stephen (ConocoPhillips Company) | Willis, Mark (ConocoPhillips Company)
Near-surface anisotropy can distort P-wave traveltime and amplitude analysis from deep target layers. When the target layer is azimuthally anisotropic, the traveltime/velocity variation with azimuth (VVAZ) or amplitude variation with azimuth (AVAZ) from the target layer may show anomalous behavior due to the influence of the near-surface anisotropy. This study uses two synthetic cases to analyze the effect of near-surface anisotropy on a deep anisotropic target. Our results suggest that the traveltime data (or VVAZ signals) from the target layers can be distorted significantly due to the presence of near-surface anisotropy; but the near-surface anisotropy influence may be negligible on the AVAZ signals from the deep target layer.
The transient tri-axial induction log can read formation resistivity deep with a short transmitter-receiver offset. Interpretation of the transient data is straightforward and the formation can be imaged using the time-sequential voltage responses at a receiver or the time-dependent apparent conductivity and/or apparent dip. The dip and anisotropy of an anisotropic formation are algebraically derived from the transient tri-axial induction data in a homogeneous anisotropic formation. The time-dependent apparent dip and apparent anisotropy are algebraically defined from the transient tri-axial induction measurements in layered formations. The apparent dip yields the true dip in an anisotropic formation as well as in layered formations, though it yields the zero dip in an isotropic formation. The apparent anisotropy yields the true anisotropy of the layer around the induction tool at early time and the macroscopic anisotropy within a larger volume of investigation at later time. The distance to the layer interface is identified by the transition time where the apparent dip and the apparent anisotropy change the values