In the last 25 years, only one barrel of oil has been discovered for every four used, and operations will have to become more sophisticated to maximize existing reserves.

R&D is vital, and demand for this is set to increase as the industry seeks new ways to secure sustainability. To that end, the Industry Technology Facilitator (ITF) issued a call for proposals on unconventional oil reservoirs earlier this year. Technology developers have been invited to submit solutions in response to the specific challenges specific to these reservoirs.

Key challenges were identified at a recent gathering of several member companies at an ITF Technology Challenge Workshop in Houston.

Technology challenges

Technology is required to address the following issues identified by ITF’s members:

  • Unconventional reservoir simulation;
  • Upscaling;
  • Optimized hydraulic fracturing (economics);
  • Reservoir surveillance;
  • In situ stress measurement (and downhole pressure sensing);
  • Rock and fluid physics;
  • Hydraulic fracturing fluid tracking (understanding production mechanisms);
  • Early production forecasting; and
  • Fracture imaging.

Many of these challenges relate to the difficulty the industry has in generating reliable models that help inform the decisions to drive development.

Stimulation

Operators are seeking advancements that enable fracing to be carried out with even greater efficiency and predictability. Optimizing hydraulic fracturing is crucial to the economics of field development. However, a number of issues can stand in the way of improving recovery and flow rates.

Often these problems are unforeseeable. A focus of development in this area is the gathering of data. Oil and gas companies can observe fracture geometry that differs from the intended design, and there is a need for integration of fracture density and other factors with reservoir knowledge. Fractures present within a reservoir can result in unexpected reservoir behavior, and imaging natural fractures is important in understanding their distribution and density. A major step going forward will be the development of non-microseismic methods for more accurate induced fracture measurement.

There also is a need to avoid fracturing in low-quality sections of the reservoir and to target sweet spots. Developing standards for reservoir characterization and modelling is necessary as are more robust fracturing techniques that achieve the fracture design objectives.

Fluid tracking in hydraulic fracturing and understanding production mechanisms need improving. Finding the reasons for high salinity in flowback water, tracking where missing fracturing fluid has gone, and determining the origin of toxic or radioactive species present in produced water are all key criteria.

Reservoir surveillance

A cost-effective reservoir surveillance system is needed to optimize reservoir performance through understanding fluid flow to the wells. This will increase recovery and determine the size and number of hydraulic fractures required.

Long-term monitoring solutions and surveillance methods that identify the composition of fluids over the length of the wellbore and can cope with fluid variations also are needed. Another objective is to be able to distinguish between steady-state and transient flow conditions in the well bore based on analysis of pressure and flow-rate data.

Alternative designs need to be investigated to overcome the difficulty of installing tools and sensors in openhole completions. Developing a link between simulations and reservoir and wellbore surveillance is another area identified by ITF.

Affordable and reliable downhole temperature and pressure measurement in real time while fracturing and producing also is needed. These measurements will improve the efficiency of the hydraulic fracturing job, and

real-time validation of the fracture efficiency will lead to improved control of the fracture height and distance (the stimulated reservoir volume), improved monitoring of the flow rate, and an indication of well interference. In situ stress measurement will provide insight into the stress tensor. It is hoped that development activity will lead to improved packaging of sensors for pressure and temperature measurement and better data transmission.

Rock and fluid physics

The group determined that rock and fluid physics studies need to move from the laboratory to downhole to develop “true” fluid/rock properties that can lead to an understanding of production mechanisms. Achieving “most efficient reservoir access” (through sweet-spot targeting, optimized well path, and minimizing the number of wells) will lead to maximized recovery.

A real challenge is obtaining representative in situ measurements and considering the impact of wettability. A number of related challenges include sampling to accurately represent in situ conditions, how to achieve meaningful measurements despite environmental changes (during retrieval of samples from reservoir depth), and sampling and measurement approaches that can account for the anisotropic and heterogeneous reality of the rocks at all scales.

Developing in situ testing methods for application while drilling/stimulating is one suggested approach for tackling the challenges of rock and fluid physics as well as establishing real-time downhole fluid composition measurement versus variable pressure, temperature, volume, and stress. The call also presents the opportunity to develop an understanding of real-time rock coupled geomechanics.

ITF has an ongoing project with CSM relevant to stimulation within unconventional gas reservoirs, investigating hydraulic fracture growth in fluvial tight gas sands. The project is supported by five operating companies and is undergoing a second phase of development. (Image courtesy of ITF)

Projects under way

ITF has an ongoing project with the Colorado School of Mines (CSM) that is investigating hydraulic fracture growth in fluvial tight gas sands. The project, which is undergoing a second phase of development, is supported by five operating companies.

The CSM project, 3DTIGHT, is focusing on improving the understanding of 3-D hydraulic fracture growth in tight gas sands to facilitate development in both onshore and offshore settings. It combines data from an outcrop in Northwest Colorado that is representative of fluvial architecture with hydraulic fracture modelling.

Fracture growth in unconventional reservoirs can be extremely complex and often exceeds the industry’s capability to predict it. The main outcome of this project will be to determine how different tight gas fluvial depositional environment systems, such as crevasse splays, channels, and point bars, affect hydraulic fracture growth in three dimensions. Such an understanding will lead to improvements in hydraulic fracture treatment designs and, subsequently, improved reserve recoveries.

Onshore developments will benefit from this knowledge due to an increased understanding of the necessary well spacing to recover associated reserves. Offshore developments will profit at an even greater level since downspacing in an offshore environment can be cost-prohibitive. Any improvement in the understanding of 3-D drainage patterns will aid overall reservoir management.

After the call for proposals on unconventional oil reservoirs closes Sept. 9, 2011, submitted proposals will be issued to members for review, with a final commitment to sponsor following.