A new acoustic tool has been developed to measure formation acoustic properties through casing. This measurement is important for oil and gas production in mature fields, and for wells that are cased without logging due to borehole stability issues. Conventional acoustic logging through casing in poorly bonded boreholes has been a difficult task due to the presence of overwhelming casing waves that mask the formation acoustic signal. To overcome this difficulty, we developed an acoustic tool using dual-source transmitters and the processing technique for the data acquired by the tool. This paper elaborates the operating principle of the new dual-source technology and demonstrates its application to casedhole acoustic logging. By using the dual-source design, the overwhelming casing waves from the poorly bonded casing are largely suppressed. On the basis of the casing-wave suppression and the condition that the formation is acoustically slower than casing, the formation acoustic-wave amplitude is significantly enhanced in the dual-source data-acquisition process. Subsequent processing of the data reliably obtains the acoustic velocity of the formation. The new tool has been tested in many cased wells with proven performance for various cement-bond conditions. The success of this technology makes casedhole acoustic logging an effective operation that can be routinely used to obtain reliable formation information through casing for slow to moderately fast formations.
Maleki, Masoud (Uuniversity of Campinas UNICAMP) | Danaei, Shahram (Uuniversity of Campinas UNICAMP) | Davolio, Alessandra (Uuniversity of Campinas UNICAMP) | José Schiozer, Denis (Uuniversity of Campinas UNICAMP)
Permanent Reservoir Monitoring (PRM) in systems deep-water settings provide on-demand snapshots for hydrocarbon reservoirs at different times during their production history. Delays in the interpretation turnaround of 4D seismic data reduce some benefits of the PRM. These delays could adversely impact the decision making processes despite obtaining information on demand. Using fast-track approaches in 4D seismic interpretation can provide timely information for reservoir management. This work focuses on a fast-track 4D seismic qualitative interpretation in PRM environment, with the aim of choosing the best seismic amplitude attribute (4D) to use. Different seismic attributes are extracted and the one with high signal-to-noise ratio is selected to carry out the 4D qualitative interpretation. All 4D signals are juxtaposed with well production history data to increase confidence in our interpretation. The selected attribute can be interpreted and used for the foreseeable life of field. This workflow has been developed and applied on post-salt Brazilian offshore field to choose the best seismic attribute to conduct the 4D seismic qualitative interpretation.
Fiber optic technology has been used in several wells at an oilfield to measure strain to monitor overburden deformation. The application of this technology involved a series of bench tests and field tests to gather some key learnings to enhance well design, well construction, and fiber optic operation. Prior to installation of the fiber optic, a series of bench tests were conducted to evaluate the coupling of fiber with the capillary lines to determine its impact on the measurement of strain. The testing demonstrated that anchoring the fiber at the top and bottom of the capillary line was sufficient to hold the fiber in place and enabled the effective measurement of strain along the length of the well, which was proven when applied to field conditions. To enhance well design for strain measurement, several wells had fiber optic capillary lines installed on the inside and outside of casing to investigate the potential dampening effect due to fiber being located inside a string of casing. This was used to determine the optimal casing string to install fiber optic to measure strain in the overburden. Additionally, a novel concept was utilized in the well design that involved using the fiber optic capillary clamps as borehole centralizers, which resulted in equipment and rig cost savings. The details of the bench tests, well design, operational experience, and their associated lessons learned are presented.
The seismic inversion method using the seismic onset times has shown great promise for integrating real- continuous seismic surveys for updating geologic models. However, due to the high cost of seismic surveys, such frequent seismic surveys are not commonly available. In this study, we focus on analyzing the impact of seismic survey frequency on the onset time approach, aiming to extend the advantages of onset time approach when infrequent seismic surveys are available.
To analyze the impact of seismic survey frequency on the onset time approach, first, we conduct a sensitivity analysis based on the frequent seismic survey data (over 175 surveys) of steam injection in a heavy oil reservoir (Peace River Unit) in Canada. The calculated onset time maps based on seismic survey data sampled at various time intervals from the frequent data sets are compared to examine the need and effectiveness of interpolation between surveys. Additionally, we compare the onset time inversion with the traditional seismic amplitude inversion and quantitatively investigate the nonlinearity and robustness for these two inversion methods.
The sensitivity analysis shows that using interpolation between seismic surveys to calculate the onset time an adequate onset time map can be extracted from the infrequent seismic surveys. This holds good as long as there are no changes in the underlying physical mechanisms during the interpolation period. A 2D waterflooding case demonstrates the necessity of interpolation for large time span between the seismic surveys and obtaining more accurate model update and efficient data misfit reduction during the inversion. The SPE Brugge benchmark case shows that the onset time inversion method obtains comparable permeability update as the traditional seismic amplitude inversion method while being much more efficient. This results from the significant data reduction achieved by integrating a single onset time map rather than multiple sets of amplitude maps. The onset time approach also achieves superior convergence performance resulting from its quasi-linear properties. It is found that the nonlinearity of the onset time method can be smaller than that of the amplitude inversion method by several orders of magnitude.
Within a single field geophysical survey results always have a significant amount of data with a considerable variability and heterogeneity. This allows to classify geophysical data as a Big Data. Data scientists and software developers are increasingly recommending the use of machine learning techniques for data processing and interpretation. ML algorithms allow one to extract the most complete amount of useful information, reduce time costs, minimize the subjective factor in the decision-making process, etc. Early testing of these approaches began in the 60s, active practical implementation consisted in the 90s due to the large-scale implementation of seismic studies in 3D CDP modification 1. The emergence of new algorithms, modifications of the original data, the development of computational resources support the relevance of this topic at the present time. In seismic data interpretation machine learning approaches provide high performance in the process of automatic horizons picking, fault tracing, seismic facies analysis, sesimic inversion, reservoir prediction, etc. At the stage of seismic facies analysis application of the ML algorythms is especially effective since in the process of multiattribute classification the initial dataset increases severalfold in accordance with the number of calculated attributes 5-7, 9, 10.
Ghazali, Ahmad Riza (PETRONAS) | Abdul Rahim, M. Faizal (PETRONAS) | Mad Zahir, M. Hafizal (PETRONAS) | Muhammad, M. Daniel Davis (PETRONAS) | Mohammad, M. Afzan (PETRONAS) | A. Aziz, Khairul Mustaqim (PETRONAS)
The key objectives were to achieve better seismic resolution and spatial delineation in very heterogeneous reservoirs. We decided to supplement simultaneously the surface 3D multi component seismic acquisition by placing additional fiber optic live receivers in the subsurface via a "True-3D" experiment without shutting down the oil production. The most cost-effective method to snapshot this wavefield propagation downhole is by utilizing fiber optic Distributed Acoustic Sensing (DAS). The borehole 3D VSP data were acquired by sharing the surface OBN nodal survey airgun sources. This is an important experiment for the field in the future so that the need to halt insitu field production for 4D time lapse monitoring will not be required if the S/N is acceptable by using this method. This permanent installation of fiber optic cables has become our ears on wells, not only for 3D DAS VSP but for proactive monitoring of the field, ensuring optimum production performance throughout the life of the field.
Obtaining high-resolution borehole images in oil-based mud (OBM) from logging-while-drilling (LWD) tools has been made possible through the recent development of ultrasonic imaging technologies. High-resolution acoustic impedance images enable reservoir evaluation through the identification of faults and fractures, bedding and laminations, and assessment of rock fabric. This paper presents examples of high-resolution images from a 4¾-in. ultrasonic imaging tool in OBM applications and discusses their value in assessing reservoir quality.
This paper provides details of field trials of an LWD ultrasonic imaging tool for use in boreholes ranging from 5¾ to 6¾ in. High-resolution images detailing both borehole caliper and acoustic impedance in both vertical and horizontal wellbores are shown, illustrating the high level of formation evaluation now available when OBM is used. The methodology used to address the impact of tool motion on the impedance images will also be covered. The value of real-time data on borehole stability assessment will be discussed, along with additional applications made possible from the real-time data, such as wellbore placement enhancement.
Both real-time and recorded data from field trials show the potential applications for the ultrasonic imaging tool. High-resolution impedance images covering different formations and lithologies show bedding planes and laminations and enable the calculation of stratigraphic dip, while the identification and assessment of fractures show the potential to aid operators during the development of their hydraulic fracturing program. Borehole caliper and shape assessment in real time can be used to modify the drilling parameters and to adjust mud weight, while providing an input into geomechanics assessment.
The LWD logs presented illustrate the factors that influence data quality and the methodology used to ensure high-resolution images are available in both vertical and high-angle wellbores using OBM. A direct comparison between data acquired while drilling and while re-logging sections is shown, highlighting the repeatability of the measurement while also illustrating the impact of time-since-drilled on the borehole. A comparison with wireline measurements highlights the potential for using the high-resolution LWD images as an alternative to wireline, where cost and risk of deploying the wireline may be high.
The ability to collect high-resolution images in OBM in wellbores ranging from 5¾ to 6¾ in. ensures that increased reservoir characterization is possible, leading to significant improvements in determining the viability of unconventional and other challenging reservoirs. The high-resolution amplitude images are comparable with those available on wireline technologies, and the real-time application of borehole size and shape for input into wellbore stability and geomechanics analysis ensures that common drilling hazards can be avoided.
Zones of increased fracture density related to the tectonic disturbances and connected to the protrusions and recesses of the consolidated basement were identified with the application of seismo-dynamic analysis of the seismic data. This is done for the first time on Povkhovskoe oil field located in Western Siberia.
Daily and monthly rates of the producing wells in relation to their location within the geological structure were analyzed. The analysis showed a pattern of increased well productivity by more than 2 times when approaching the areas with high density of fractures. At a distance of more than 500 m from the tectonic disturbances the fluid inflow rates significantly decrease and the performance of hydraulic fracking provides only short-term effect. The deterioration of the reservoir properties is due to a decrease in the value of the reservoir rock permeability because of the decrease in the proportion of fractures and the predominance of the pore space. Reservoir type changes from fractured or fractured-porous reservoir type to porous-only type.
The dependence of high oil saturation of the productive formation from the presence of the tectonic disturbances was recorded. Exploitation of producing wells confirms the assumption of oil moving along the sub-vertical zones of destruction and contributing to the primary target Upper Jurrasic-1 reservoir. Drilling of sidetracks from low oil rate and high water saturation wells in the areas with increased fracture network identified by seismo-dynamic analysis showed a high efficiency of the operations leading to a high-rate production including a substantially lower water-cut oil production (up to 5% of water) at the site where the surrounding production wells have water-cut of 99-100%. Meanwhile, reservoir characteristics of the Upper Jurrasic-1 formation are identical. Based on the results of research identified were prospective deposits for the drilling of production wells on the edges of the hydrocarbon accumulation in areas with high fracture density and suggested were the borehole sidetracks of wells that are plugged and abandoned.
Thus, the detailed structural and tectonic structure of the basement surface and the Jurassic sediments allows to select complex, small-scale geological features, which will be very prospective for the detection of small oil deposits, to specify the location of exploration wells, to start the search for deposits in areas of sub-vertical degradation in the Middle and Lower Jurassic sediments, basement rocks in areas with overlying hydrocarbon deposits already in development. Identifying zones of high density fracturing, including those associated with horizontal shear zones, allows to adjust the contour outlines of the alleged existing deposits and to discover prospective areas with the increased permeability. Described zones and areas are likely to be located close to faults originating in the basement.
Al-Jenaibi, Faisal (ADNOC - Upstream) | Shelepov, Konstantin (Rock Flow Dynamics) | Kuzevanov, Maksim (Rock Flow Dynamics) | Gusarov, Evgenii (Rock Flow Dynamics) | Bogachev, Kirill (Rock Flow Dynamics)
The application of intelligent algorithms that use clever simplifications and methods to solve computationallycomplex problems are rapidly displacing traditional methods in the petroleum industry. The latest forward-thinking approaches inhistory matching and uncertainty quantification were applied on a dynamic model that has unknown permeability model. The original perm-poro profile was constructed based on synthetic data to compare Assisted History Matching (AHM)approach to the exact solution. It is assumed that relative permeabilities, endpoints, or any parameter other than absolute permeability to match oil/water/gas rates, gas-oil ratio, water injection rate, watercut and bottomhole pressure cannot be modified.
The standard approach is to match a model via permeability variation is to split the grid into several regions. However, this process is a complete guess as it is unclear in advance how to select regions. The geological prerequisites for such splitting usually do not exist. Moreover, the values of permeability and porosity in different grid blocks are correlated. Independent change of these values for each region distortscorrelations or make the model unphysical.
The proposed alternative involves the decomposition of permeability model into spectrum amplitudes using Discrete Cosine Transformation (DCT), which is a form of Fourier Transform. The sum of all amplitudes in DCT is equal to the original property distribution. Uncertain permeability model typically involves subjective judgment, and several optimization runs to construct uncertainty matrix. However, the proposed multi-objective Particle Swarm Optimization (PSO) helps to reduce randomness and find optimal undominated by any other objective solution with fewer runs. Further optimization of Flexi-PSO algorithm is performed on its constituting components such as swarm size, inertia, nostalgia, sociality, damping factor, neighbor count, neighborliness, the proportion of explorers, egoism, community and relative critical distance to increase the speed of convergence. Additionally, the clustering technique, such as Principal Component Analysis (PCA), is suggested as a mean to reduce the space dimensionality of resulted solutions while ensuring the diversity of selected cluster centers.
The presentedset of methodshelps to achieve a qualitative and quantitative match with respect to any property, reduce the number of uncertainty parameters, setup ageneric and efficient approach towards assisted history matching.
In extended reach and horizontal wells, it is critical to maintain borehole quality and stability to ensure efficient drilling and for the running and installation of completions. Categorising the risk of borehole degradation is becoming an important aspect of the well planning process. The quality of the borehole is affected primarily by geomechanical or drilling practices, which can significantly impact the life cycle and completion expenditure/cost of a well. We show examples of how recently available, high-resolution, acoustic logging-while-drilling (LWD) borehole image logs have enabled detailed characterisation of borehole shape to the extent that we can visualise and analyse all contributors to borehole stability. LWD measurements also enable the use of time-lapse logging; comparing images from the first pass with repeated logging runs at later stages in drilling to look for degradation in conditions of the borehole shape. These data can be used for several new or existing applications that can be split into two main categories: 1. drilling hazards – degrading borehole shape profiles, identification of borehole breakout and washed-out sections and 2. completions hazards – cement volume calculations, identification of trajectory and small-scale irregularities that could impair liner placement. These applications use zonation to describe all ranges in borehole trajectory, borehole shape and image artefact features for coding of the well during or shortly after drilling. This scheme is then combined with a geomechanics-centric integrated risk management workflow which provides an improved well planning process by identifying potential drilling and geological risks in each of the planed well sections. Pre-drill risk identification combined with visual verification of the borehole condition enables quick decision making for drilling and potential de-risking of subsequent wireline logging and completions operations, thereby allowing safe, predictable operations with minimal NPT, from drilling to completions. The enabling technology of high-resolution LWD acoustic imaging has made possible the visualisation of borehole shape features in detail previously not possible in either water or oil-based mud systems.