Methodology to Increase Gravity Drainage Rate in Oil-Wet/Mixed-Wet Fractured Reservoirs

Physical Sciences : Petroleum

Available for licensing

Inventor

  • Kishore Mohanty, Ph.D. , Petroleum and Geosystems Engineering

Background/unmet need

Many oil-wet/mixed-wet fractured reservoirs employ gravity drainage to recover oil. Gravity drainage is enabled by the density difference between the injected fluid (e.g. gas, steam, water, surfactant) and oil. The effectiveness of gravity drainage is often controlled by the thickness of the pay zone, even though vertical barriers are present in the matrix and the matrix is broken up into several layers. The oil drains out of the top layers into vertical fractures, but re-imbibes into the layers below because the matrix is oil-wet/mixed-wet. The drainage rate in such a reservoir is inversely proportional to the total height of the entire pay zone, which in most cases means it is very slow.

Invention Description

Researchers at The University of Texas at Austin have designed a method to increase the oil drainage rate during gravity drainage in these oil wet/mixed wet reservoirs. In a gravity-drainage process, a small amount of chemical (called a rate enhancer) will be injected into the fractures as an aqueous solution or foam before or during gas or steam injection from the top (or water/surfactant-water injection from the bottom). The treatment can be repeated periodically if the effect of the chemical degrades over the long drainage time. This novel method, while increasing the rate of drainage, also prevents the re-imbibition of oil onto lower layers in fractured reservoirs.

Benefits/Advantages

  • Improves gravity drainage oil rate
  • Can use any water-wetting chemical as wettability agent (surfactants, chelating agents, acids, etc.)
  • Can choose an appropriate wettability agent based on the reservoir rock, oil, and brine at the reservoir temperature
  • Novel wettability alteration strategy of the fracture-matrix interface

Features

  • Periodic injection of a rate enhancer during gravity drainage increases oil drainage rate
  • Wettability altering agent changes wettability to a more hydrophilic state in select regions
  • Prevents oil re-imbibition into the underneath matrix layers
  • Overcomes inversely-proportional relationship between drainage rate and pay zone height

Market potential/applications

Markets and Markets Research reports that the global hydraulic fracturing market is expected to grow to $72.6 billion at a compound annual growth rate (CAGR) of over 11.8% by 2019. Hydraulic fracturing is essential for producing the most oil and gas possible from shale formations, in which the necessity for drilling unconventional shale formations is driven by the depletion of onshore oil fields. As of 2014, North America is the largest and most influential market in hydraulic fracturing due to its abundance of available shale reserves.

Development Stage

Lab/bench prototype

IP Status

  • 1 U.S. patent application filed