DRILLING & PRODUCTION

A system for calculating petroleum fluid pressure, volume, and temperature (PVT) properties from downhole wireline formation tests, named PVTMOD, combines GeoMark Research geochemistry and reservoir fluid database technology with Baker Atlas' reservoir characterization instrument (RCI) service.

Real-time reservoir fluid properties

A system for calculating petroleum fluid pressure, volume, and temperature (PVT) properties from downhole wireline formation tests, named PVTMOD, combines GeoMark Research geochemistry and reservoir fluid database technology with Baker Atlas' reservoir characterization instrument (RCI) service. The system provides real-time reservoir fluid properties that are used by operators to estimate the economic recovery from a reservoir and in the planning of production facilities. Real-time PVTMOD results are communicated from the wellsite to the user's office and field locations through the Internet.

Conventional PVT lab results, which often take several months to be delivered, are based on the analysis of a limited number of downhole hydrocarbon samples retrieved by wireline sampling or drill stem testing. This system provides a real-time method for generating fluid properties for each reservoir unit of interest. Another advantage is the ability to evaluate zones that are not sampled due to well conditions or high rig costs.

The system using the RCI service provides an efficient, cost-effective method for estimating hydrocarbon physical properties and collecting quality formation fluid samples. By providing real-time downhole PVT simulation at the wellsite, the data can accelerate reservoir and production planning as well as the economic evaluation of new reservoirs.

The system, active in the Gulf of Mexico, will be expanded to other geographic regions within the next nine months.

Micropolymer fracturing fluid

A new fracturing system enables real-time viscosity control, allowing operators to adjust a fracturing fluid's formulation almost instantaneously based on observed treatment responses such as surface pressure. The key to this system is the viscoelastic fluid, which uses Halliburton's MicroPolymer material, a substance that is 25 to 30 times smaller than conventional polymers. In developing this new system, the fluid process was re-engineered with a focus on desired rheology, real-time operations, and the environment.

For years, water-based polymers, guar, and its derivatives have been mainstays for conventional fracturing fluids, providing a low-cost highly controllable rheology frac fluid. But even with the highest quality, guar-based, low-polymer fluid system and highly efficient breaker, a high percentage of the fracture conductivity can be lost to frac fluid damage, leading to poorer-than-expected well productivity following fracture stimulation.

In field trials, this fluid system created highly productive fractures with low conductivity damage while still providing excellent fluid loss control and superior proppant transport properties. The fluid system exhibits little degradation with time and temperature, and also shows low salinity sensitivity and real-time controllable rheology.

The fluid system can provide polymer-like rheology and fluid loss control without high molecular weight polymer chains. This is accomplished by creating a high molecular weight transitory-linked polymer once short molecular units are combined with a reversible-linking component. Since this transient-linked polymer is pH reversible, it requires no polymer chain breakers. After pumping has stopped, the freshly fractured formation alters the injected fracturing fluid to the naturally occurring pH of the formation thereby delinking the fluid. The solution pH and linker quantity can determine the strength of the transitory linkages. It is also possible to control the linking time by adjusting the fluid's pH, which can provide increased control for long pumping time treatments.

Because the short-chain molecules are highly concentrated, no hydration time is required and only simple dilution with fresh water is needed to prepare the fracturing fluid. Advanced blending equipment can deliver the short-chain molecule concentrate directly to the blender so that it can be diluted at any required ratio. Modifying the dilution ratio changes the base fluid viscosity, making real-time rheology control feasible. This control can be a major advantage during the early stages of a fracturing treatment because viscosity can be increased to overcome wellbore tortuosity and initiate the fracture. During the treatment, rheology can also be adjusted to control fracture height growth and the formulation can be ramped based on formation cool-down response.

The ability to control fluid properties in real time is a significant advancement in fracturing, as it allows the fluid rheology to be changed based on real-time treating responses. On a typical frac treatment, the adjusted fluid will reach the formation within the pipe travel time rather than the 20 to 60 min it can take for conventional fluids to adjust on surface and reach the formation. The user gets the right amount of the right fluid type at the time it is needed for the best fracturing results, according to the company.

Because only fresh water is stored and used on the wellsite, the chances of spillage and the brine disposal costs for unused water are reduced. Since most of the additives are premixed with the highly concentrated short-chain molecules, the total number of liquid additives required on-site is dramatically decreased compared to conventional fracturing fluids. Premixing also reduced the risk of site contamination. Finally, monitoring and metering fewer liquid additives can aid in fluid quality control.

Reservoir analysis

A new analytic application allows reservoir managers, petroleum engineers, geologists, financial experts, and other contributors to portfolio decisions to pool and analyze large quantities of disparate technical and business data to better inform the multi-million-dollar production decisions oil and gas companies face daily. An analytics application provider, Spotfire Inc., has released DecisionSite for reservoir analysis, the product of a joint development agreement with Chevron-Texaco's Global Technology Services Co.

The oil and gas industry relies for its exploration and production decisions on teams focused around assets, typically groups of 10 to 30 members, made up of experts in the varied specializations needed to manage the portfolio of oil assets in a given geographic region. This system for reservoir analysis helps these teams make better collective decisions, the company says, by easily interacting with large amounts of otherwise incompatible technical and business data presented in a single analytical environment. Better decisions ultimately mean oil and gas companies can allocate resources to higher-producing wells, thereby improving the long-term value of the asset portfolio.

The system has wide applicability to multiple disciplines in an oil and gas company. Over the past year, Spotfire and ChevronTexaco have co-staffed a project team to interview internal experts within ChevronTexaco to specify opportunities for analytic applications. The Spotfire product development team collected product requirements and developed prototypes working directly with a ChevronTexaco asset team to ultimately produce this system for reservoir analysis.

In oil and gas, acquiring data can be very expensive, yet some data may not be used effectively because of the difficulty to access and quickly integrate data with business inform-ation needed for a decision. This can be especially true in the day-to-day decisions that asset teams need to make.

Asset team decisions involve a universe of business and technical factors, including geology, geophysics, facilities configuration and cost, transportation, political boundaries, tax and royalty structures, product pricing, available capital and more. Discipline-specific tools exist to analyze each of these factors, but lack the ability to enable the knowledge sharing and collaboration the asset team organization was designed to encourage. This system allows team members to navigate information derived from multiple specialist tools, even outside of that individual's specialty. Because the application is based on the system guided analytics platform, teams can perform constant "what-if" portfolio analysis, capturing and deploying best practices for problem solving while making team-level decisions.

With hundreds of thousands of dollars riding on key decisions, the oil and gas industry is strongly motivated to speed cross-domain decision-making. This system leverages existing investments in data, tools and best practices from each individual expert, the company says, so that they can work as one cohesive unit of deeply informed decision makers.

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