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.

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.

Steamflood with conventional vertical wells results in poor vertical sweep efficiency and steam breakthroughs when it is applied to heavy oil reservoirs. The use of horizontal producers provides a larger contact area with the reservoir resulting in a better drainage and therefore enhancing the well productivities by improving the steam sweep efficiency.This study explores and compares the efficiencies of steamflooding in an improved version of an inverted 7-spot pattern with a vertical injector in the center and horizontal producers versus vertical producers in a representative numerical geological model from the Orinoco Oil Belt.The simulation of the complex displacement processes 1 combined with the well configuration results in challenging computational issues. As a result of the mechanisms involved in steamflooding, including oil viscosity reduction, steam condensation into hot water, large mobility ratio differences in the displacement processes, etc., the Grid Orientation Effects (GOE) could be significant. A grid selection process was performed to reduce grid orientation effects comparing the steam displacement in a Cartesian grid versus those from an unstructured Perpendicular Bi-sector (PEBI) grid.Once the grid was established, sensitivity analyses were carried out to define the optimal design parameters to improve sweep efficiency and reduce recovery times. The parameters analyzed were: (1) placement of the horizontal producers within the vertical reservoir pay, (2) placement of the toe and heel of the horizontal producers, and a sensitivity analysis to (3) bottom hole flowing pressure, and (4) steam injection rates.Reservoir conditions were also studied to explore the effects of: (1) pay thickness, (2) variation of horizontal permeability, (3) permeability anisotropy generated from geostochastic distributions, (4) and previous cold production, in the overall process performance.The use of PEBI grids allowed to model in a more accurate way complex thermal-compositional displacement processes involving horizontal wells not aligned with the orthogonal Cartesian axes, and demonstrated that steamflooding using horizontal producers offers the potential to improve conventional schemes achieving higher oil recoveries from heavy oil reservoirs.

The chief objectives of this investigation were to study, theoretically and experimentally, the sweep efficiency and oil recovery for steam injection into a five-spot pattern. Experimental runs and mathematical simulations were conducted for this purpose. The experimental models used consisted of glass bead packs simulating a quadrant of a five-spot pattern, over-lain and underlain by heat-conducting formations, and fitted with thermocouples to determine the temperature distribution during the steamflood. Effects of oil viscosity, saturation, injection rate, and heat losses on oil recovery and sweep efficiency were studied.The mathematical model developed was a combination of the concept of flow in channels and a formation heating model, allowing for a variable injection rate, differences in the properties of the overburden and the underburden, and variations of relative permeabilities with temperature. The mathematical model was used to simulate the ex-perimental runs. Good agreement was observed. It was found that, for the oils tested, sweep efficiency in steam floods was 40 to 50 per cent, depending chiefly on th; viscosity of the oil used. The oil recovery, however, was large, being of the order of 80 per cent, because of the hot waterflood ahead of the steam zone. The sweep effr ciency was relatively insensitive to initial saturations and the steam injection rate. Formation thickness and steam quality were found to have an appreciable effect on oil recovery. For low-quality steam, the ,-steamflood degener-ates rapidly into a hot waterflood. ADAFEL C. RINCON is ebief of the reservoir studies group in the Ministry of Mines and Hydrocarbons of . TIIE PAST FEW YEARS, pattern steamflooding has gaine(I considerable popularity as a secondary or tertiary oil recovery method for both viscous and lowviscosity crudes. Currently, however, few methods for calentating-oil recovery by a steamflood are available.Marx and Lagenheim and Willman et al. 1 2 1 did pio-neering work in this area by proposing mathematical models for calculating the volume of the formation heate(i an(i the oil recovery from a radial steamflood. Davies, Silberberg tnd Caudle proposed a method for I)redicting oil recovery from a five-spot steam-flood, bastd on the approximation of the streamlines by straiglit lines radiating from the injection well, and then (converging to the production well. The I)res-ent Nx-ork ])roposes an improved method for predicting the ])erformance of a steamflood in a five-spot pat-trn, Lisin,, a combination of Higgins and Leighton's"', Marx and. Langenheim's Willman et al.'s"', and Ramey's techniques adapted for a steamflood in a five-slot pattern. Also, extensive experimental results are liserited, designed to test the model, and also to obtain data on pattern steamflooding, with regard to oil viscosrLy, distillability, injection rate, ete. Fair to good agreement was obtained between the model pre-(nctit)ns and the experimental results. On the whole, it wis found that the sweep efficiency in a five-spot steamflood is consi...