The offshore state of Sarawak in Malaysia contains many mature wells that were completed 20-30 years ago with dual-strings and multiple packers to exploit the many layers of sand packages. The wells that were designed to exploit the main sand packages are currently depleted and producing at high water cut. The operator is now considering ways of exploiting the smaller intermediate sand packages in these wells. In many cases, this requires oriented perforating through one completion string while avoiding shooting another completion string that is still producing. Oriented perforating using analog orienting devices that were previously deployed has many operational problems that on several occasions have led to abandoning jobs, and ultimately deferment of additional production. As such, this has led to many of these mature wells that require oriented perforating being left unexploited for many years. The arrival of a new digital orienting device is expected to open the path to better exploitation of the intermediate sand packages.This paper is a case of deployment of this device for PETRONAS Carigali in Sarawak, Malaysia which required collaboration with the service contractor at many stages, from planning and characterizing the device responses in various completion configurations in Sarawak, to writing standard operational procedure and contingency planning, and to real-time decision making during operation.The results of operation of this device on two wells in Sarawak are also presented, as is how the collaboration in the planning stages contributed to their successes.While the success paves the way for future exploitation of the intermediate sand packages for PETRONAS Carigali, the exercise also provides a reference for similar operations in other places, from the point of collaboration and technicality of the service itself. IntroductionThe offshore state of Sarawak in Malaysia contains many mature fields that were drilled 20-30 years ago. Most have many packets of sands and were completed with dual-strings, multiple packers, and sliding side doors (SSD) to avoid commingling different oil zone reservoirs. If all the sands were to be produced from the same well, that would require a very complex completion string, something that could be very expensive or would be limited by the availability of technologies at that time. Furthermore some of the sand packets are small in comparison with the main sands. As such, only the main sands were perforated and produced in an optimized completion string. Fig. 1 and Fig. 2 show two typical dual completion wells in the state of Sarawak.

Uncertainties in hydrocarbon saturation calculations have to be quantified and managed prior to STOIP/ GIP estimations for economics evaluation of reserves. There are numerous statistical tools to do the quantification of variances. This study compares the root-mean-squared (RMS) error in the results of saturation-height-function (SHF) as functions of input variances against Markov Chain Monte Carlo (MCMC) treatment of the same. Deterministic aggregation of errors in SHF (or variances of results -S w -) via RMS against the simulations of solutions of SHF with randomly selected inputs of a given range (MCMC) are compared to evaluate the error margins in deterministic against probabilistic treatments of the same data and equations.RMS-driven error estimations are more sensitive than Monte Carlo (MC) simulations of errors when a large error in one of the inputs may produce disproportionate weight on the formulations originating from partial derivatives of the equation. However, Monte Carlo approach has also theoretically questionable treatment of data due to conceptual violation of independency of the individual variables in subject equation because of inter-dependencies of permeability to porosity in our models. However, these potential issues are circumvented by the proper range for the systematic errors (due to measurement and treatments) in RMS and by using Markov Chain method in MC, respectively.The comparison of variances (error margins) from RMS versus MCMC methods are presented for different forms of SHF (e.g., Leverett-J and modified forms). This study presents the ranges of S w determined from two different approaches as avenues of selecting the more appropriate methodology for a specific case. The width of the confidence intervals from RMS is proportional to the RMS-driven error margins while Monte Carlo simulation of the S w by SHF also yielding the boundaries where the outcome of a specific J-function would lie.

Petrophysical evaluation of a given formation is not complete without looking into all means of exploitation of resident hydrocarbons. With this intent, we studied the hydrocarbon potential of the subject formation via conventional Petrophysics and identified only the possibility of recovering residual-oil(Sro). The remaining question and the objective of this study was the quantification of Sro that can make EOR sweeping of residual-oil economically viable or cost-prohibitive. It is a well-known phenomenon that additional residual oil (Sro) may be present below the conventionally defined oil-water-contacts as a function of geologic and hydrodynamic conditions. In addition, the oil-wet formations force the contact to be below Free-Water-Level leaving a sizable Sro "Stranded Oil" in or below the transition zone. The zone of "Stranded Oil" can be quite thick and economically viable for tertiary EOR techniques if there is a sufficient recoverable volume. To confirm the presence and quantify the saturation of residual oil, we used diffusion-T2 intrinsic (DT2) maps from Nuclear Magnetic Resonance NMR log. The DT2 technique was challenged with a possibility of superimposed signals from residual oil and the filtrate from Synthetic-oil-based-mud (SOBM). However, an appreciable viscosity difference between residual formation oil and SOBM-filtrate made it possible to differentiate the NMR signals from SOBM and residual oil based on different diffusion characteristics. We had all possible reasons for having a thick zone of Sro. Either mechanical (tilting of the basin) and/or compartmentalization due to re-formed seals or later movement of water to the lower part of the oil accumulation were present. Hence, looking for a thick zone of Sro that was generated by reasons beyond the capillary behavior was justifiable. However, the quantification and derivation of Sro profile based on clearly identified residual-oil signals revealed a Sroprofile that failed to justify the formation as a future EOR sweep-zone. DEFINITION We would like to define "residual oil" as the oil left in the formation that cannot be recovered by conventional means (including water-flood) under practical and field-driven average conditions (as the optimum draw down pressures and completion requirements). The residual saturation of hydrocarbons depends on the horizontal and vertical sweep efficiencies, structural and geological constraints, heterogeneities of the petroleum system and the microscopic displacement efficiency. However, including the "field-averageconditions" and "conventional means" to the definition, makes it relevant to the case under study. METHODOLOGY SELECTION Microscopic pore-scale attributes(wettability, pore throats, irreducible-wetting-phase saturations, displacement pressure, etc.) control the flow before it is affected by the macroscopic constraints (seals, tight streaks) or enhancers (fractures, channels). Core analysis can shed a light to the Sro with certain limitations. Most of the residual oil saturation from conventional cores under-call the actual residual oil saturation due to expulsion of oil (bleeding) and shrinkage of oil as pressure decreases during the removal of core from formation to the surface. There are methods of corrections, but the Sro determination from core analysis still has high uncertainties if one considers the filtrate invasion (or coring fluid) of the core. The pressure coring addresses these issues, but we did not have pressure-coring for this case. Recent "tracer testing" workflows have also been effective measures of Sro. We did not have tracer testing for the subject study either.