TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn recent years, expandable sand screen (ESS) has become popular as a sand exclusion mechanism in oil and gas sand face completion. ESS provides sand control through the bridging of formation sand on the screen that is sized to retain formation sand while allowing formation fines to pass through. The deployment of Cased Hole ESS (CHESS) in The Shell Petroleum Development Company of Nigeria Ltd (SPDC) since the late 90's has been mainly as a remedial sand control mechanism post-workover operation to replace the previous sand control mechanism if any or to complete over a new interval. The successful deployment of CHESS in over 30 conduits in the Niger Delta by SPDC over the years has come with various challenges and lessons learned leading to improvements in the selection criteria, deployment methodology and procedure, clean-up and operational envelope of usage. This paper presents some of the results and the lessons learned in CHESS deployment in SPDC and offers an insight into the selection and usage of CHESS as a sand control mechanism especially in well remedial operations to prolong well life and optimise hydrocarbon recovery.

The process of sandstone acidizing is fraught with the danger of further damaging the reservoir. The odds of increasing formation damage is raised if standard acidizing practices are not followed primarily due to non-technically related issues like logistics. This paper reviews the stimulation of two low-pressure oil producers and another oil producer, which was previously producing below potential. Standard practice indicates that a HF based system be flowed back or lifted with nitrogen to reduce the risk of additional formation damage due to factors including emulsion / sludge / secondary precipitate formation. For these case histories, the residence time of the acid in the reservoir was between 18 hrs to 96 hrs due to the non-availability of nitrogen and poor well inflow. The remarkable aspect of these operations was that there was no evidence of further impairment in all the wells. In fact, two of the wells demonstrated superior performance after production rate stabilized. These successes are partially attributed to the unique chemistry of the retarded acid system, favorable rock mineralogy, exhaustive lab testing / field QC, the presence of an acidic over flush and the use of additives that prevented formation of emulsion and sludge. This acid system can be used in depleted / low GOR reservoirs where over-displacing is a poor option in the absence of flow-back aid and also for single stage acidizing in low carbonate sandstone reservoirs. This paper attempts to follow through the process of candidate selection with a focus on nodal analysis. It also defines the factors affecting success rates in the stimulation of depleted reservoirs, offers a superior acidizing system for mitigating the effect of deviations from standard acidizing practices and reinforces the possibility of single step sandstone acidizing (with a brine cushion ahead) especially in low carbonate content sandstone.

Evaluation of hydrocarbon recoveries from a field with limited geological, engineering, and geophysical data has a huge amount of uncertainty for each possible outcome. Understanding the implications probability of success (POS) of the sequence of events, can help managers make informed decisions on a field development strategy using a decision tree.A decision tree, is a decision support graphical representation that uses a tree-like graph or model of decisions and their possible consequences, including chance event outcomes, resource costs, and utility. This, if effectively used can assist in making difficult decisions by reducing them to a series of simpler or less emotionally laden, choices. This paper details, the results of the use of a Decision Algorithm for the optimization of a gas field development strategy with only one well drilled and no production data. The optimization was carried out following the re-interpretation of the seismic and well data, which resulted in a significant change in the structure and subsequent update in the static and dynamic characterization of the hydrocarbon bearing reservoirs.

Gas Cap Blowdown (GCBD) involves a process of depressurizing the gas cap of an oil reservoir to produce the associated gascap volumes, more often after the oil rim has been depleted of significant oil production. Thus, the optimal development plan for such reservoirs carries both large technical and commercial uncertainties and a robust technical evaluation is required to underpin commercial decision. In most moderate to strong aquifer drive reservoirs, the displacement of gas as the oil rim moves upwards into the gas cap causes residual oil losses with trapped gas. This paper details the integrated study of a gascap development of oilrim reservoir initially developed by twelve (12) oil wells and with over 40 years of production history; and overlained with an undeveloped huge gascap with M-factor, m>1.6. The reservoirs comprise of number of communicating blocks by a series of nonsealing synthetic faults and a number of nonsealing transverse faults of up to 200 ft throw. Full scale 3-D simulation models; using the Shell's proprietary 3D dynamic modelling application; Modular Reservoir Simulator (MoReS) were deployed to assess subsurface uncertainties and history match reservoir performance of the reservoirs. The impact of resaturation of original gas cap volume and timing of gascap blowdown on the ultimate recovery of the gascap were exhaustively evaluated. Optimal development of the gascap was assessed against a range of technical uncertainties which then formed the basis for development of other reservoirs in the field that were not subject to the full uncertainty assessment. From the results of the subsurface uncertainty analysis and extensive history match, three (3) gas wells targeting the gascap were proposed to develop the reservoir and optimum timing of gas cap development was evaluated, while concurrently producing the remaining oil volumes with exising wells. In addition, the results from sensitivity analysis evaluated different timing for commencement of gascap blow down and the associated incremental recoveries. Also, for residual oil in the presence of gas, reduced range of values upto 30% of the oil-to-water residual saturation results due to the different blow down timings.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe process of sandstone acidizing is fraught with the danger of further damaging the reservoir. The odds of increasing formation damage is raised if standard acidizing practices are not followed primarily due to non-technically related issues like logistics.