Waterflood recoveries from certain areas in this large, thick carbonate reservoir were below expectations. An integrated (geological, petrophy:ical, and engineering) study was undertaken to (1) develop a geological-petrophysical model covering the areas of interest, (2) evaluate past reservoir performance, (3) predict future performance for various operating plans, and (4) make appropriate recommendations based upon technical and economic considerations. It was concluded that low oil recovery resulted primarily from low to very low formation permeabilities, injected water channeling because of fracture treatments administered during primary production, net pay intervals still behind pipe (mainly in producers), and limited control of injection/production well profiles. Results of the study indicated that oil recovery could be increased significantly by infill drilling/waterflood expansion.However, the most attractive plan from an economic viewpoint was to open the unperforated net intervals in existing producers and injectors and to monitor/improve flow profiles. Other enhanced recovery methods were not attractive because of either low permeability or low oil gravity.

The benefits of UnderBalanced Drilling-UBD are now widely understood and revealed. However, the impact of UBD on well productivity/injectivity is still elusive.Few papers have documented historical applications of UBD and a recent focus has been to quantify UBD benefit through productivity increase comparisons, or productivity improvement factors-PIFs against field averages. Yet, comparative analyses are questionable. A process named Suitable Underbalanced Reservoir Evaluation (SURE) has been developed to identify UBD prospects and to quantify the potential well productivity/injetivity benefits of a UBD operation.SURE is a simple, fast and reliable way to accurately evaluate the suitability of an UBD operation for reservoir performance. Introduction When UBD succeeds, it work wonders: discovering hidden production zones, speeding drilling by eliminating lost circulation and differential sticking & increasing rate of penetration, improving production by reducing formation damage, and providing real time reservoir evaluation.The result - enhanced ultimate recovery and improved net present value. Yet too often, UBD fails to live up to its potential either because unsuitable reservoirs are drilled or inappropriate drilling technology is applied. The key to selecting appropriate reservoir candidates for UBD is achieving a balance of technical, safety and economic factors. SURE Process SURE is a novel process that was developed in partnership with industry experts in reservoir engineering, formation damage and risk analysis. The SURE process is designed to give engineers the ability to quantify the technical and economic value of applying underbalanced drilling (UBD) techniques. The overall architecture of the SURE process is illusterated in Figure 1. The process consists of two phases: Phase I, Reservoir Screening Analysis (RST)™ The ‘quick-look’ screening study is the first step in the SURE process. The screening study uses the Reservoir Screening Tool (RST) software to:Evaluate and rank a reservoir's risked probability of being successfully exploited with underbalanced drilling and completion techniques as opposed to conventional drilling and completion techniquesCompare candidate reservoir(s) with analogs proven to be suitable to underbalanced drilling.Identify the best potential underbalanced candidate from a given portfolio. In the RST software, a number of modules are incorporated through which the candidate reservoir is run. These modules combine classical formation damage theory with vast experience of underbalanced analog reservoirs. After several thousand Monte Carlo simulation iterations, RST produces a risked suitability score for the candidate reservoir. The final score calculation is summarized as a summation of the individual modules and indices that make the reservoir a candidate and subtracts that score by applicable exclusionary factors. The end result is a risked RST underbalanced candidacy score with a distribution indicating its degree of certainty and variability.Table 1 Shows the key components considered for underbalanced candidacy. UB Candidacy Indices and ModulesDamageability: The damageability index estimates the severity of the formation damage that can be expected from conventional drilling operations. The potential for formation damage mechanisms such as aqueous phase trapping, fines migration and solids invasion are evaluated.Effect of Damage on Production and Recovery: Depending on the reservoir, the effect of formation damage on production and ultimate recovery can vary. These indices consider reservoir characteristics such as drive mechanism, reservoir fluids and mobility ratio to estimate its impact.Treatability: The Treatability index considers the probability of success using common stimulation techniques versus a properly executed UBD well.

Two- and three-dimensional simulation studies have been done to evaluate waterflood oil recovery in a 40-acre 5-spot pattern using horizontal and vertical well systems. The three-dimensional simulation results indicate that the parameters considered, i.e. vertical permeability-horizontal permeability ratio, injection and production rates, and reservoir thickness have little effect on waterflood oil recovery for a particular water-oil mobility ratio. For both vertical and horizontal well systems, oil recovery decreases with increasing mobility ratio. It is concluded that the mobility ratio is the dominant parameter affecting waterflood oil recovery, in line with the experimental results of Craig, Geffen, and Morse1 for conventional waterfloods. Waterflood oil recovery using a horizontal well system is shown to be higher than that obtained by using a vertical well system. A correlation has been developed which expresses volumetric sweep efficiency in a hypothetical 5-spot pattern as a function of mobility ratio. This correlation would be useful for estimating waterflood oil recovery for the ranges of reservoir parameters considered. Introduction Oil recovery and production rate from a reservoir may be improved by waterflooding. The conventional waterflood technique, which has been used for decades, involves flooding the reservoir using various patterns of vertical injection and vertical production wells. The most common waterflood pattern is the five-spot. Extensive literature exists on the types, design, performance prediction and operation of conventional waterfloods.2–4 Improvements in horizontal well technology during the last decade have made the use of horizontal wells a technically and economically attractive alternative to vertical wells under certain conditions. Horizontal wells have been shown to be superior to vertical wells for purposes of:productivity improvement,intersection with and drainage of vertical-fracture networks,reduction of gas or water coning, andincrease in sweep efficiency.5 Theoretically, production from all reservoirs can be improved through the use of horizontal wells. However, to benefit from the use of horizontal wells, both vertical and lateral reservoir characteristics must be well known, including the reservoir drive mechanisms and fluid characteristics. Horizontal wells can be applied in any phase of oil recovery: primary, secondary, and tertiary. The drilling of horizontal wells may be considered as an alternative to:infill drilling with vertical wells, andfracturing. In all cases, the objective is to increase the economic recovery and production rate of oil and gas. Previous researchers have carried out simulation studies to investigate several important aspects of horizontal wells. These include the partial penetration of the well in the horizontal direction within the drainage area, the positioning of horizontal wells between the top and the bottom of the reservoir, and the effect of reservoir permeability anisotropy. However, most previous studies have focused on the performance of a single horizontal well, omitting the interaction of the horizontal well with other wells.6–10 In spite of numerous papers on horizontal wells, especially during the past six years, little information is available on waterflooding with horizontal wells. Norris et al11 presented a review on the reservoir engineering aspects of horizontal wells. Of the 84 references cited in the paper, eight were in EOR applications involving steamflooding, but none involved waterflooding. There is, therefore, a need to study how horizontal waells, used as injectors and/or producers, would affect waterflood performance.

fax 01-972-952-9435. AbstractThe South Region of Pemex Exploración & Producción (PEMEX E&P) is running a key development plan to improve the reservoir management, well productivity and ultimate recovery of all fields in the region. A fundamental part of this project is gathering reliable well production data on real time and on regular basics. The South Region of PEMEX E&P in cooperation with the technical team of PEMEX E&P performed a full study of available technologies in well testing to select a system that meet the needs of the region while simplifying the field logistic and minimizing environmental impact. PEMEX E&P selected the use of multiphase flow meters (MPFM). The program scope includes 8,064 measurements at well heads and collection manifolds during three years. The preparation and use of this MPFM program for multi-rate well tests was carried out with variable gasliquid ratio flowstream and systems capable to measure all types of flow regimes in fields producing from heavy oil to gas condensates. This paper describes the lessons learned about the practical reliability, accuracy, and operability of the MPFM meters. The paper illustrates with field results the benefits of implementing the multiphase metering in the region. MPFM meters have proved to be a reliable system to measure well productivity.

Waterflood recoveries from certain areas in this large, thick carbonate reservoir were below expectations. An integrated (geological, petrophy:ical, and engineering) study was undertaken to (1) develop a geological-petrophysical model covering the areas of interest, (2) evaluate past reservoir performance, (3) predict future performance for various operating plans, and (4) make appropriate recommendations based upon technical and economic considerations. It was concluded that low oil recovery resulted primarily from low to very low formation permeabilities, injected water channeling because of fracture treatments administered during primary production, net pay intervals still behind pipe (mainly in producers), and limited control of injection/production well profiles. Results of the study indicated that oil recovery could be increased significantly by infill drilling/waterflood expansion.However, the most attractive plan from an economic viewpoint was to open the unperforated net intervals in existing producers and injectors and to monitor/improve flow profiles. Other enhanced recovery methods were not attractive because of either low permeability or low oil gravity.