Oil production in presence of a bottom aquifer is one of the most challenging issues in reservoir engineering. In most cases water coning happens very quickly and the influx of water restricts oil production and limits recovery. The problem is even more difficult when the oil is heavy because the viscosity contrast is large. In some cases horizontal wells may be used to improve the situation but when reservoirs are thin and the oil is viscous even horizontal wells are of limited use. This paper presents the challenges and potential solutions for Enhanced Oil Recovery in heavy oil reservoirs with bottom aquifer. Existing literature is reviewed for field cases of EOR experience with bottom aquifer for chemical as well as thermal processes (SAGD, steam injection as well as In Situ Combustion). In the case of chemical EOR the chemicals may be lost to the aquifer; for thermal recovery the bottom water can act as a heat sink and affect and steam oil ratio. Some in-situ combustion projects have been successful in such settings but in every case the outcome is the same: the economics of the project can be affected. The paper contains some previously unpublished data of polymer injection in a heavy oil pool with some limited bottom aquifer; for the most part it is a review of the existing literature which may prove useful to practicing engineers who are faced with the issue of developing heavy oil resources in the presence of bottom aquifer.

The purpose of this paper is to report the methods used and results of the Rubiales

Rubiales and Quifa are the Colombia's major heavy oilfields (oil gravity ranges from 11.3 to 14.4° API) with a current oil production of more than 260 MSTB with an oil viscosity ranges from 370 to 730 centipoises. Horizontal well technology is used to drill through unconsolidated sandstones with an active and strong aquifer, under primary depletion. Since 2006, 604 horizontal producer wells have been drilled and completed using slotted liner in open hole. The high water production rate from the beginning of the operation in the horizontal wells is the main problem to be controlled in the Rubiales and Quifa fields, due to the high cost of produced water treatment and other factors. Water production is inevitably associated with the oil production; however one of the biggest challenges is to delay the water production as much longer as possible. Rubiales and Quifa actually have a large number of closed wells that have reached its economic limits, mainly by high water production. This production imbalance is being addressed in the new horizontal wells, using inflow control devices (ICDs). The ICDs is placed in each screen joint to balance the production influx profile across the entire lateral length and compensate the permeability variation and therefore the productivity of each zone. In 2012, a pilot test has been designed and implemented in Rubiales field with three horizontal wells using passive ICDs completion. The performance of the ICD's is found to reach the highest cumulative oil production compared to neighboring wells. The main purpose of this paper is to detail the selection process design and results evaluation for the use of the passive ICDs in horizontal wells at Rubiales and Quifa Fields, heavy oil reservoirs.

Colombia's Oil production is around 1.1 million barrels per day (bpd), where 57% is from Heavy Oil fields. Current oil recovery is in the 15% to 17% range; with targets to increase it up to 50% through different methods. A typical reservoir exhibits hydrocarbon viscosity variations in hundred of centipoises, with formation water salinity typically below 5000 ppm and heterogeneities driving a complex fluids distribution. Since the low amount of salt in these environments prevents low frequency conductive devices for contrasting water versus hydrocarbons, where additionally, resistivity profiles are ambiguous to assess fluids mobility in the reservoirs. In this context, the incorporation of additional physics of measurements opens a new perspective in the reservoir evaluation in Llanos basin, by reducing uncertainties and helping in the initial reservoir characterization. The new generation of wireline measurements supporting the present job is represented by multifrequency dielectric propagation, radial magnetic resonance and dynamic testers, in addition to the conventional triple combo logs. Since good-oil bearing rocks (high porosities and permeabilities, very clean sands, high oil saturations) do not guarantee oil production (very high water cut is likewise common), the identification of movable oil and free water volumes in low salinities is mandatory. Understanding its distribution across sands is also a critical factor in heavy oil environments. As a resistivity and salinity-independent reservoir evaluation approach, the combination of dielectric dispersion and radial magnetic resonance, provides a valuable sensitivity for the evaluation of displaced oil, free and irreducible water, viscosity and rock quality variations. Dielectric Dispersion is the variation of relative permittivity and conductivity versus frequency, enabling pore fluids determination. With a dielectric analysis at two depths of investigation, integrated with NMR-based diffusion mesurements, a direct identification of movable oil under filtrate invasion conditions and free water presence is achieved. The correlations encountered between the dielectric dispersion is encouraging; whereas a better understanding on the movable oil occurrence and estimation of the fluid to be moved during production is achieved. Discussions with case studies in Llanos Basin are presented in this paper.