This study aims to evaluate a wide variety of thermal processes in Boyacá area, located in Guárico state in the Southern flank of the Orinoco River, Basin of Venezuela, which holds an extension of 1247 km2 of extra heavy oil with an API Gravity between 4–8 (API: 4–8), porosities between 25–32% and permeabilities of 2–15 Darcies. Block 06 produced through 7 wells, two of which did not produce, while others two produced by Cyclic Steam Stimulation (CSS) as a test. Results from these tests indicate success in one well which had an accumulated oil production of 26179 STB in one cycle. Synthetical correlations were used in order to estimate fluid and rock properties, considering data obtained from nearby blocks. Geoestatistical model resulted from a refinement of the entire Boyacá area. This new model was classified in three ranges of continuous net sand thickness. First step involved an analysis of this block using."screening criteria" to determine which thermal process was appropriated to apply. As a result, steams flooding based technologies were recommended due to their power to increase the recovery factor in heavy and extra heavy oil reservoirs, providing the required heat content of steam (1200BTU/lb). A following step was building sector models in order to simulate the production history in one of the CSS wells, to simulate each thermal process and to optimize operational parameters. Subsequently, CSS and SAGD (Steam Assisted Gravitational Drainage) were simultaneously simulated. According to these simulations, it is feasible to maximize the recovery of this block up to 30% using this kind of technology. Furthermore, the best economical indicators were obtained through a combination of CSS+SAGD resulting in a net present value of 1521 M$, internal return rate of 15%, operational costs of 16 $/Bbl for an economical horizon of 20 years.
A meandering system where sandbodies produced are complex, so that fluvial deltaic reservoir consist of channel belt sandbodies with highly variable permeability patterns pose a significant challenge for further development of a mature oil field in the Southwest Venezuela. To obtain an optimal strategy a multi-disciplinary reservoir characterization study was carried out. This study combined all available data (geophysics, geology, petrophysics, and engineering) into a 3D stochastic geo-model to build a reservoir simulation model, many sensitivities with grid size and reservoir description in fluvially dominated deltaic facies were undertaken. These sensitivities included various assumptions on sand content of main producing horizons, sandbody dimensions, permeability distribution, and continuity of flood plain acting as vertical barriers in some reservoir areas. All these sensitivities were tested during history matching as alternatives to reach a history match. Drilling locations and some exploitation strategies were made in order to improve the oil recovery factor through closing some wells for several periods (3 months - 6 months) and then opening those wells, this technique helped to decrease the water production rate and increased slightly the oil production rate. The associated economic evaluations were based on simulated forecasts while connected volume calculation was made for the chosen realization.
The necessity of knowing formation pressure is crucial to classifying pressure regimes for better understanding in well planning and to de-risk potential abnormal pressure conditions before any future field development wells are drilled, consequently minimizing operational cost. Wireline formation pressure testing has been a useful and reliable technology, that has evolved to confront the challenge of ultra-low permeable reservoir conditions by innovating and improving pump capability, accuracy in pressure measurements, automated control and the implantation of Formation Rate Analysis (FRA) intertwined with an Artificial Intelligent tool. In any pressure testing, the key factor is to be able to withdraw volume from the formation to generate a disturbance on formation pore pressure that a pressure gauge can measure. In the past this has been a difficult task in ultra-low permeable zones. The new generation of wireline tools are capable of withdrawing volume from ultra-low permeable reservoirs, with mobilities lower than 0.01mD/cP. This has been made possible by utilizing control of the pump speed down to 0.0003cc/s which then gives the operator the ability to test ultra-tight formations without the need for inflatable packers. By pulling down the pressure at an extremely low rate and using Artificial Intelligence to control the rate by knowing the formation rate, a proportional amount of volume can be extracted without calling it a tight test. During the operation by observing the rate, and making sure the pump is not oscillating, which indicates the formation rate is lower than the lowest rate the pump can withdraw, the test can be validated for formation flow and the pressure transient of the build – up can be analysed to confirm that at least spherical flow is observed. Once reservoir communication has been confirmed and by analysing drawdown and build-up pressure versus volume withdrawn and implementing the FRA equation, the reservoir pressure can be back calculated by considering isothermal compressibility and FRA slope. This paper highlights the best technical approach to quality check and quality control these tests, showing examples of various wells, where the technique has been used to predict a formation pressure, which can be used for further use for field development, drilling optimisation and production profiles. These pressures would never have been possible using static rates and volume.
Reservoirs declination in Apure State, Southwestern Venezuela, demands a huge technical effort in reservoir modeling when finding drilling opportunities to increase recovery factor and maintain oil production at attractive economical levels. One of these reservoirs, Escandalosa Inferior of La Victoria Oilfield was discovered by LVT-18 in 1991 with 38 MMSTB of STOOIP and in 1998, the last of its four producing wells was closed, reaching a recovery factor of 14%. An Asset Team revised and integrated geophysical, geological, petrophysical and production data to update Esc-Inf static model in 2005. No robust sedimentological model could be built because of cores absence; however, a facies and later a property distribution was designed with the help of well logs, regional knowledge and geostatistics. The resulting static model led to visualize the opportunity to drill a horizontal well in the highest attic of the structure to reactivate the reservoir. STOOIP calculation for this new model yielded a value of 13 MMSTB with 7.8 MMSTB of recoverable reserves and 2.5 MMSTB of remaining reserves, which could be extracted by the new well and finally obtain a recovery factor of about 60%. The dynamic model showed a reaccommodation of fluids due to its 5 years of closure, and certified the current presence of oil in the attic where the well was previously visualized. The prediction made by the simulator for a 5 years scenario, with a production of 650 STBD, highlighted the economical feasibility of drilling this well. Nowadays, the successful well LVT-46H is still active with 2 MSTBD and has accumulated 0.245 MMSTB, since its completion in 2006. These results validate the methodology presented in this work where data integration, the use of geostatistics and reservoir simulation are the main key for reactivating declined reservoirs and maintaining oil production. Introduction La Victoria Oilfield is located 40 Km to the west of Guasdualito Village, Apure State, Southwest of Venezuela and 6 Km to the East of the Colombian - Venezuelan boundary (see Figure 1). Escandalosa Inferior Reservoir, belonging to this oilfield, is a cretaceous unit (1) constituted mainly by massive and consolidated sandstones with a very continuous thickness in the whole oilfield of up to 140 feet, with few intercalations of shales, featuring porosity values between 20 and 25 % and permeability values between 0.5 and 3 darcies (see Figure 2). Escandalosa Inferior Reservoir had been reporting by the end of 90's high water cuts in the only four producing wells since its discovery, which is a contrasting fact in relation with its remaining reserves of 15.8 MMSTB following the official data yielded by the reservoir static model built in 2001. These high water cuts progressively caused the closure of the four producing wells, the last of which was closed in 1998, setting the reservoir to inactive with a recovery factor of only 14%. Under this perspective, no well could be workovered and even less drilled in this reservoir, without an appropriate structural reinterpretation. In 2003, a 3D seismic survey was completely processed and available for interpretation, and this was the starting point of the structural reinterpretation for generating a 3D static model supported by geostatistics techniques, well logs interpretation and the knowledge of regional geology since no robust sedimentological model was available due to core data absence in this reservoir. This new static model would then be used in a reservoir numeric simulation software in order to know the current state of the reservoir in terms of oil saturation after 7 years of inactivity, and in order to forecast the productivity behavior and future profitability of the prospect wells that probably could be highlighted by the static model and could help increase the reservoir recovery factor.
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