Steam injection projects consume considerable amounts of energy to generate steam. Understanding where the heat goes at various times and places during the process provides the means to improve the performance of a project. Enhancements can be achieved integrating an energy balance analysis from the steam generator through the injection network, the reservoir, the producing network and the journey of the produced fluids to the separator. This investigation presents a workflow to analyze the integration of surface and reservoir systems for a Steam Assisted Gravity Drainage (SAGD) project, to properly estimate energy transfers in the various components of the system thus providing information to improve project planning and enhance both the oil recovery and the economics of the project. The elements considered in the systems were: boiler, heat exchanger, steam trap, steam injection and well networks, reservoir heat usage, heat losses to the over- and under-burden, production wells and surface networks. Parameters such as completion schemes, artificial lift and boiler-wellhead distances were also analyzed. Results show that surface-reservoir integration, using reservoir and network simulators, is a powerful tool to estimate heat losses in steam injection projects, helping to understand and successfully optimize their performance. The integration allowed the detection of steam quality variations at injection wells at various times during the process as a function of injectivity changes. Adequately insulated production wells under certain circumstances could produce under natural flow for some FAJA types of reservoirs. However, artificial lift methods had to be incorporated into other completion schemes to compensate for high heat losses and their correspondent increased oil viscosities that imposed higher pressure drawdowns in the production and surface gathering networks. The SAGD processes analyzed were energy efficient in spite of retaining in the reservoir less than a third of the energy from the steam. In all the scenarios, oil production was considerably greater than the fuel consumed to generate steam. The paper shows how the analysis of steam injection processes integrating surface, well and subsurface mechanisms allows the identification of critical components of heat losses to optimize the design and operations to maximize oil recovery and reduce energy consumption. Introduction Energy efficiency in oil industry operations has become an important issue to take into account in project planning. Global energy requirements are increasing faster than new oil reservoirs are discovered and the situation is aggravated by the continuous decline from mature conventional oil reservoirs. Heavy and Extra Heavy Oil production seem to be an answer to the energy demand in the years to come. However, Heavy Oil (HO) and Extra Heavy Oil (X-HO) production require especial techniques, more analysis and higher investment in order to produce energetically efficient and economically viable operations.
El Bunduq reservoir is located in the offshore area of Abu Dhabi and Qatar. The field was shut-in in July 1979 due to production with high gas-oi 1 ratios. Pressure differences of 200-400 psi between the flanks and the central part of the reservoir were sti 11 present almost four years after the field was shut-in. A comprehensive reservoir engineering study determined that the reasons for this behavior were the deteriorating qualities of the reservoir rock downstructure and the presence of a tar mat around the field.After the field behavior was history matched, model studies of a representative sector of the field indicated that peripheral waterflooding would recover 1 ess than 15 percent of the 001 Pin a peri od of 30 years.However, pattern injection recoveries were calculated to be at least twice as high.Several full field alternatives were investigated to optimize the development of the reservoir under a pattern waterflood. This paper summarizes the various studies that led to the acceptance of the idea of pattern development over peripheral injection, as a result of the unique characteristics of this field.
The Orinoco Belt (Faja) in Venezuela contains one of the largest resources of heavy and extra-heavy oil in the world. Due to the production decline of conventional light crude, projects must focus on increasing the recovery of heavy and extra-heavy oils using thermal and non-thermal methods. Steam-based thermal recovery processes are more efficient in low pressure reservoirs; however due to their depth, the initial pressures of the reservoirs in the Faja are relatively high, in the range of 600 to 1,500 psi with viscosities typically greater than 2,000 cp. For the above reasons, it is important to decrease the pressure of the reservoirs with primary production techniques to facilitate the economical implementation of steam injection based methods. The initial production of heavy and viscous oils can be accelerated by the adequate use of downhole heaters that, by providing energy to the vicinity of the well, decrease oil viscosity and increase the oil production rate. A consequential advantage of using downhole heaters as a preamble to a steam injection process is that they accelerate early production and reservoir pressure decline while the equipment associated with steam injection, including steam boilers, insulated pipes and proper facilities are designed, ordered, installed and commissioned. This paper analyzes the effects of downhole heaters as a stimulation method through the use of a numerical model of a representative field in the Ayacucho area of the Orinoco Oil Belt. The study has been divided in three parts. The first part relates to the use of downhole heaters in thick sands, stimulating both vertical and horizontal wells in the reservoir. The second one evaluates the temporary application of downhole heaters in horizontal wells for a limited period of time to accelerate production and pressure decline, followed by a full implementation of a Steam Assisted Gravity Drainage (SAGD) process. The third part of the paper covers basic economical analyses perfor ed using estimated capital and operating expenses with oil production curves from each case, to assist in the comparison of their worth using common economic parameters. Introduction Heavy oil reservoirs are increasingly being developed because of their great potential, the necessity to compensate for the decline of conventional oil production and by the favorable opportunities created by current high oil prices that make these kinds of projects more profitable. Countries like Canada, Russia, and Venezuela are directing their efforts to develop this kind of unconventional oil reservoirs. The technology to produce heavy and extra-heavy oil is still under accelerated development to meet the challenges to efficiently produce and procure the proper facilities for thermal operations.
The Orinoco Heavy Oil Belt (Faja) has been exploited under primary recovery techniques using mainly horizontal, fishbone and multilateral wells. This cold development can only recover between 6% and 9 % of the considerable original oil in place existing in the area. Owing to the high viscosities, widely different formation thicknesses and heterogeneities found, the implementation of different thermal recovery methods is necessary.This project covers a feasibility study considering the Horizontal Alternating Steam Drive (HASD) process geared to increase the recovery efficiency of heavy oil within the Faja reservoirs. The process is based on a repetitive pattern using horizontal wells acting alternatively as oil producers and steam injectors. The recovery mechanism is a combination of horizontal steam flooding between wells and cyclic steam stimulation of each of the horizontal wells in the pattern. Properly implemented, HASD could be more efficient than classical cyclic steam injection and more effective than direct steam flooding.In contrast to the Steam Assisted Gravity Drainage process (SAGD), HASD uses single horizontal wells cyclically switching between injection and production phases. The steam chamber generated while each well is injecting is laterally driven by the pressure differentials created by adjacent producers, forming a sweeping front between wells. Injectors are converted to producers (and vice versa) providing heat directly to the zones where production will occur gradually extending the steam chambers to the entire reservoir region. Thus, the impact of steam is not that of a simple well stimulation, but also achieves an effective sweep in the vicinity of the producers while decreasing oil viscosity and improving oil drainage.This project is based on the numerical simulation results from a representative model from one of the Faja main blocks using Eclipse Thermal applied to medium thickness sands in the 20-50 net ft range.A five-horizontal well array set up was used as the model to assess this fairly new thermal recovery technique. During the investigation, different scenarios were analyzed to obtain a generalized step-by-step optimization procedure for the process under the specified fluid and reservoir conditions. Sensitivity analyses were performed considering the relative positioning of the horizontal well placement in the reservoir column; different injection sequences; varying the duration of each injection cycle; various injection rates; and lengths of the horizontal reach of the wells.The results of this investigation can be used as a reference to optimize the performance of the HASD process for sand bodies of medium thickness.
The work presented in this paper describes the evaluation and stepwise optimization process for a Steam-Assisted Gravity Drainage (SAGD) project using a representative sector model from a field with fluid and reservoir characteristics from an eastern Venezuela formation.Due to the complexity and number of variables involved in the process, SAGD presents multiple challenges from the design and analysis phases to its final implementation. The objective of this investigation was to understand the impact of key parameters in the process specific to the selected area and to understand the effects on the recovery factor in these reservoirs, which have previously produced with primary recovery mechanisms.The study touches upon the effect of the component grouping for fluid characterization. A preliminary work consisted of reducing the original 14 components identified in the existing Pressure/Volume/Temperature (PVT) analysis into 2 and 3 pseudocomponents and comparing the stability and results using both fluid characterizations to attain reasonable running times in the simulation process.Once the fluid behavior was successfully recreated and the model was set up, a sensitivity analysis was conducted using thermal simulation. The parameters analyzed were vertical well spacing, injection steam rate, well flowing pressure, and horizontal length of the well pair. The effect on the oil recovery from the angle of dip in the reservoir and the orientation of the well pair with regard to the direction of dip were also briefly analyzed.The conclusion presents a highly improved configuration for the SAGD well-pair array that resulted in trebling the oil recovery attained by the initial well arrangement.
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