This paper discusses technical challenges and technology development opportunities associated with developing and producing offshore heavy oil (OHO) reservoirs, with emphasis on projects in cold or deep waters. The paper addresses how the reservoir and fluid characteristics will impact reservoir characterization, development concept selection, well construction, reservoir performance, artificial lift requirements, flow assurance, and operations. The applicability of common onshore heavy oil practices to OHO developments will be discussed. Emerging technologies and technology development opportunities will also be discussed. The material presented in this paper will be of particular interest to technology development personnel and asset team personnel who are in the appraisal or concept selection stages of a project; however, additional information is provided which may also be valuable later in the project life.

Formation damage was simulated by injecting completion fluid into cores and conditioning at 380°F (193°C) overnight. Low hydrofluoric (HF) acid concentrations from 0.05- to 0.1% blended with 10% acetic (HAc) effectively removed the damage. Some other acid systems we tested also worked well. Acidizing did not reduce the measured compressive strengths of the cores; however, microscopic analyses showed layers within the cores may have been seriously weakened.

Effective fracture treatment distribution to stimulate and obtain production from all perforation clusters is a key goal for success in unconventional reservoirs. The objectives of this work were to assess the impacts of multi-cluster stage perforating design parameters and execution uncertainties on treatment slurry distribution, production, ultimate recovery, and offset well interference for unconventional reservoirs. A stochastic perforation breakdown and slurry injection model and a conceptual reservoir simulator were used to investigate treatment slurry distribution, production, and ultimate recovery impacts. The design parameters in the analysis were clusters per stage, cluster spacing, maximum proppant concentrations, perforation diameter, and number of perforations per cluster for both fixed- and variable-shot cluster designs. Uncertainties evaluated included perforation breakdown percentage, perforation shot phasing for non-oriented carriers, perforation hole diameter growth from erosion, and formation permeability. As part of the analysis, the authors defined and used a new dimensionless quantity—the Slurry Distribution Number (Nsd)—that potentially fills a gap as no standard industry definition exists for perforation cluster efficiency. Nsd successfully correlated perforating design changes with slurry distribution outcomes. The authors used the results to identify strategies to mitigate uncertainty impacts, obtain more predictable outcomes, and achieve improved production results. Novel information is presented that can assist perforating design optimization for unconventional reservoirs. In addition to introducing Nsd, the authors show perforation carrier phasing and shot phasing within the casing are generally not the same for decentralized carrier systems. The authors demonstrate how to model the perforation breakdown and stage stimulation process using a combination of published geomechanics, perforation erosion, and perforation flow resistance models. Lastly, the authors describe future study opportunities for perforating uncertainties and design parameters.

The paper provides an update on recent advances for, and summarizes global experiences with, dendritic acidizing methods, aka acid tunneling. The scope of the paper includes both Coiled-Tubing (CT) deployed and non-CT methods, and discusses process limitations, candidate selection criteria, job design factors, operational learnings, risks, and surveillance requirements and opportunities. The paper contains a comprehensive review of published information for three different tunneling methods and relevant information for several other tunneling methods. The literature information is supplemented by, depth, temperature, and pressure records for the three processes which are discussed in detail. Execution factors such as logistics required, length of time required, and volumes of acid and other fluids used are also compared for three methods. Previous papers have focused on only one of the methods, whereas the authors will discuss acid job optimization, process risks, and surveillance requirements for multiple acid tunneling methods in substantially greater depth than have past authors. The three methods detailed in the paper are all viable but may have different niches. Differences in the job counts for the different methods are easily explained by differences in process vintages, execution speeds, and depth limitations. Previous optimization efforts were focused on tunnel creation but not acid job effectiveness in terms of the wormholes generated adjacent to the tunnels; however, some progress is now being made in that regard. There are differences in the processes regarding pushing or pulling the jetting nozzles into the tunnels, and differences in resulting tunnel trajectories. Pre-job caliper data are more critical for one of the processes than for the others, and there are significant differences in ability to measure or control tunnel direction. The tunneling tools have different sizes, but when tool size alternatives are available, the larger tool sizes offer no clear advantages to the operator. Useful risk mitigation measures are also discussed in the paper. The paper includes a comprehensive bibliography to facilitate further examinations of the technology alternatives by other petroleum industry professionals.

This paper was prepared for presentation at the 1998 SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, 27-30 September 1998.