Tight Gas Fracturing Technology and Patent Report
- 1 Background
- 1.1 Introduction
- 1.2 Tight Gas
- 1.2.1 Conventional and Unconventional Reservoirs
- 1.2.2 Properties of Tight Gas
- 1.2.3 Map of unconventional reserves (Shale,Tight,Coalbed methane) in the world
- 1.2.4 Distribution of Tight Gas across the world
- 1.2.5 Recovery of Tight Gas
- 1.2.6 Challenges for Tight Gas Recovery
- 1.2.7 Taxonomy for various technical challenges in tight gas recovery
- 2 Methodology for Patent Search
Global demand for natural gas is increasing day by day as due to rapidly growing gas market of developing countries. As more nations are switching to environmentally cleaner fuels to maintain the economic growth and reducing the impact of increasing high oil price. Natural gas is emerged as an excellent environmentally clean fuel as it emits 43% fewer carbon emissions the coal and 30% fewer emissions than oil for each energy delivered. In order to fulfill the increasing demand of energy requirement and reducing greenhouse gas emission. “The quickest and cheapest way to cut CO2 emissions from the global power sector is to grow the presence of natural gas,” said Shell’s exploration Chief Malcolm Brinded in a speech late last year. Shell-Malcolm Brinded
Global Natural Gas Demand
According to the U.S. Energy Information Agency (EIA) latest report the global demand for natural gas is expected to grow significantly as more nations are switching to environmentally cleaner fuels such as Natural Gas. Majority of the rapidly growing gas markets are in emerging economies in Asia, particularly India and China, the Middle East and South America. EIA also shows worldwide natural gas demand grew by 57 Bcf/d from 2000 to 2007, nearly 25%. The EIA also projects global natural gas demand to grow over 40 Bcf/d by the year 2015, and projects a further growth in demand of over 50 Bcf/d by 2025.
Bentley R. W., 2002 of The Oil Depletion Analysis Centre London studied on Global oil & gas depletion: An overview. It shows that the world’s production of conventional hydrocarbons will soon decline. Global conventional oil supply is currently at political and physical risk. This is because the sum of conventional oil production from all countries in the world, except the five main Middle-East suppliers, is near the maximum set by physical resource limits. A large investment in Middle-East oil production is needed to overcome this physical risk, and to fulfill the increasing demand of hydrocarbon across the globe. Figure 2 Shows the global conventional oil distribution of the world’s, conventional oil that has been consumed (dark shading), and the currently discovered reserves (light colour). The figure uses industry (proved and probable) data for reserves (not public domain ’proved’ reserves), and excludes oil yet to- find. The major concluding points from this figure shows the world is about halfway through its effective recoverable resource base and North America has burnt about three-quarters of its recoverable conventional oil resource.
For conventional gas, since less gas has been used so far compared to oil, the world will increases its dependability to gas as oil declines. Figure 3 Shows the global conventional gas distribution of the world’s, conventional gas that has been consumed (dark shading), and the currently discovered reserves (light colour). The figure uses industry (proved and probable) data for reserves (not public domain ’proved’ reserves), and excludes oil yet to- find. The major concluding points are Europe has a little way to go before its gas peak, and the world as a whole is about halfway to its gas peak. When the ’clocks’ on this figure tick round to perhaps 8 or 9 o’clock, gas decline sets in with the decline likely to be fairly steep.
Present scenario shows that with the physical resource limits and depletion of oil there is exponential increase the demand of gas. The global peak in all hydrocarbons (oil plus gas) is likely to be in about 10 or so years. Thus there is do or die situation for development of unconventional reservoir across the globe for avoiding the situation of energy crisis in the world. http://greatchange.org/ov-bentley,global_depletion.pdf Global Depletion-Bentley
Natural Gas Distribution
Worldwide Natural gas resources shows North America contain the largest reserves of 300 Trillion cubic meters in which unconventional resources is around 230 Trillion cubic meters. Former Soviet country shows second largest reserves of 270 Trillion cubic meters in which unconventional resources is around 140 Trillion cubic meters. China and India also contain the reserves of 160 Trillion cubic meters in which unconventional resources is around 145 Trillion cubic meters. African countries, Latin America, Western Europe and others show the presence of Unconventional resources.
U.S. Energy Information Administration’s preview of its 2012 Annual Energy Outlook is the forecast for natural gas. EIA says that gas from shale and tight gas will account for 70 percent of the United States’ overall natural gas supply in 2035. It is clearly visible from the Figure 5 that there’s been a surge in shale gas production since roughly 2005. The major reason for this surge in shale gas production is due to surge in new hydraulic fracturing and horizontal drilling techniques, which helps in unlocking vast shale gas formations in states including Pennsylvania, North Dakota and Texas. And similar development is dawning in Ohio and other states too of North America.EIA-Shale report
- Tight gas refers to natural gas reservoirs locked in extraordinarily impermeable, hard rock, making the underground formation extremely "tight." Tight gas can also be trapped in sandstone or limestone formations that are typically impermeable or nonporous, also known as tight sand. In other words, the pores in the rock formation in which the gas is trapped are either irregularly distributed or badly connected with overly narrow capillaries, lessening permeability or the ability of the gas to travel through the rock. Without secondary production methods, gas from a tight formation would flow at very slow rates, making production uneconomical.
- While conventional gas formations tend to be found in the younger Tertiary basins, tight gas formations are much older. Deposited some 248 million years ago, tight gas formations are typically found in Paleozoic formations. Over time, the rock formations have been compacted and have undergone cementation and recrystallisation, which all reduce the level of permeability in the rock. Tight gas-Rigzone.
Conventional and Unconventional Reservoirs
Conventional reservoirs are those that can be produced at economic flow rates and that will produce economic volumes of oil and gas without large stimulation treatments or any special recovery process. Conventional reservoir is essentially a high to medium permeability reservoir in which one can drill a vertical well, perforate the pay interval, and then produce the well at commercial flow rates and recover economic volumes of oil and gas.
Unconventional reservoir is one that cannot be produced at economic flow rates. Typical unconventional reservoirs are tight-gas sands, coal-bed methane, heavy oil, and gas shales. Unlike conventional reservoirs, which are small in volume but easy to develop, unconventional reservoirs are large in volume but difficult to develop. Increasing price and the improved technology are the key to their development and the future. Unconventional resources are probably very large, but their character and distribution are not yet well understood. It is known to exist in large quantity but does not flow easily toward existing wells for economic recovery.
Increase in cost and technological challenges when moving from conventional to unconventional gas recovery methods. Tight Gas Reservoirs--GC Naik.
- Conventional gas picture: Thin section of a conventional sandstone reservoir that has been injected with blue epoxy. The blue areas are pore space and would contain natural gas in a producing gas field. The pore space can be seen to be interconnected so gas is able to flow easily from the rock.
- Unconventional gas picture: Thin section Photo of a tight gas sandstone. The blue areas are pores. The pores are irregularly distributed through the reservoir and the porosity of the rock can be seen to be much less than the conventional reservoir.
Unconventional Gas Resources Typical unconventional reservoirs are
- Tight-gas Sands - formed in sandstone or carbonate (called tight gas sands) with low permeability which prevents the gas from flowing naturally.
- Coal-bed Methane - formed in coal deposits and adsorbed by coal particles.
- Gas Shales - formed in fine-grained shale rock (called gas shales) with low permeability in which gas has been adsorbed by clay particles or is held within minute pores and microfractures.
- Methane Hydrates – a crystalline combination of natural gas and water, formed at low temperature and high pressure in places such as under the oceans and permafrost
Properties of Tight Gas
|S. No||Properties of Tight Gas|
|1||Matrix permeability||1 µD to 0.1 mD|
|2||Porosity||3-5% to 15-20 % (effective)|
|3||No or limited natural flow||Typically the initial flow before stimulation is less than 0.5 MMscfd (~15.000 Sm3/d)|
Map of unconventional reserves (Shale,Tight,Coalbed methane) in the world
- The world map representing unconventional gas reserves in various regions. It includes Shale gas, Coalbed methane and Tight gas.
Distribution of Tight Gas across the world
|S.No||Region||Tight-Sand Gas Volume (Trillion-cubic feet)|
|4||Central and Eastern Europe||78|
|6||Union Middle East and North Africa||823|
|8||Centrally planned Asia and China||353|
|9||Pacific (Organization for Economic Cooperation and Development)||705|
|10||Other Asia Pacific||549|
Recovery of Tight Gas
The steps involved in tight gas recovery are:
- Seismic investigation: Extensive seismic data is gathered and analyzed to determine where to drill and just what might be located below the earth's surface. These seismic surveys can help to pinpoint the best areas to tap tight gas reserves. Not only providing operators with the best locations for drilling wells into tight gas formations, extensive seismic surveys can help drilling engineers determine where and to what extent drilling directions should be deviated.
- Drilling: In a tight gas formation, it is important to expose as much of the reservoir as possible, making horizontal and directional drilling a must. Here, the well can run along the formation, opening up more opportunities for the natural gas to enter the wellbore.A common technique for developing tight gas reserves includes drilling more wells. The more the formation is tapped, the more the gas will be able to escape the formation. This can be achieved through drilling myriad directional wells from one location, lessening the operator's footprint and lowering costs.
- Production Stimulation: After seismic data has illuminated the best well locations, and the wells have been drilled, production stimulation is employed on tight gas reservoirs to promote a greater rate of flow. Production stimulation can be achieved on tight gas reservoirs through both fracturing and acidizing the wells.
- Hydraulic Fracturing: Fracturing, also known as "fracing," a well involves breaking the rocks in the formation apart. Performed after the well has been drilled and completed, hydraulic fracturing is achieved by pumping the well full of frac fluids under high pressure to break the rocks in the reservoir apart and improve permeability, or the ability of the gas to flow through the formation.
- Acidizing: Acidizing the well is employed to improve permeability and production rates of tight gas formations. Acidation involves pumping the well with acids that dissolve the limestone, dolomite and calcite cement between the sediment grains of the reservoir rocks. This form of production stimulation helps to reinvigorate permeability by reestablishing the natural fissures that were present in the formation before compaction and cementation.
- Deliquification: Furthermore, deliquification of the tight gas wells can help to overcome some production challenges. In many tight gas formations, the reservoirs also contain small amounts of water. This water can collect and undermine production processes. Deliquification is achieved in this instance through artificial lift techniques, such as using a beam pumping system to remove the water from the reservoir, although this has not proven the most effective way to overcome this challenge.
Challenges for Tight Gas Recovery
- During the last decade new technologies as 3-D seismic, horizontal drilling, and improved fracture stimulation have had significant impacts on natural gas production in many tight gas reservoirs in Middle East and North Africa. Some of the challenges in this recovery are:
1) Sub-Surface Understanding
2) Formation Evaluation Technology
3) Drilling Technology
4) Completion & Stimulation Technology
5) Environmental safety
- Geomechanics and Sub-Surface Understanding: Fundamental to any improvement in performance is done by having a clear understanding of the sub-surface environment. Understanding permeability, although at very low values compared to conventional reservoirs, is a key to maximizing productive capabilities. Subtle differences in tight gas reservoir properties can result in large changes in permeability, and mark the difference between productive and non-productive intervals.Geomechanics and subsurface understanding is a critical component in understanding the nature of the formation. All companies recognise the need to use geomechanics to assess natural fracture patterns.
- Formation Evaluation Technology: The objectives of Formation Evaluation are,to ascertain if commercially producible hydrocarbons are present, determine the best means for their recovery, to derive lithology and other information on formation characteristics for use in further exploration and development. Lack of accuracy for all porosity logs. There are strong limits to the application of NMR logging in low porosity, low permeability gas bearing formation.
- Drilling Technology: The challenge in any tight gas development is to use technology to push up the estimated ultimate recovered volume per well, and the produced volumes (flow), while simultaneously pushing down costs. Specialized drilling practices, application of drill bits for less wellbore damage , Specialized drilling fluids are few challenges that is to be overcomed.
- Completion & Stimulation Technology: One of the most important areas where technology can make a difference, is the ability to make small but extensive fractures in the correct places in the tight rock (‘fraccing’). This provides the gas molecules with a passage to move more easily through the reservoir to the wellbore. Fracturing techniques use a significant amount of energy to create the pressure used to crack the rock open. The first hydraulic fracturing job to be run commercially in the 1940s required just a few hundred horsepower. More recently, in examples such as the Pinedale field, power requirements can be as high as 25,000 horsepower, and costs can represent up to 30% of the well costs. Any possibility to make this more efficient has significant cost implications.
- Environmental Safety: Drilling of hundreds of wells represents a major environmental and safety challenge. Shell is tackling this challenge and is focused on improving well performance and surface engineering, which will push the business forward in a sustainable manner. Tight Gas Developments-IGU.org, Unconventional gas-NPC.org
Taxonomy for various technical challenges in tight gas recovery
Methodology for Patent Search
A detailed search strategy was formulated to extract relevant patents in the area. Keywords were obtained from some relevant patents, journal articles, company websites and other thesauri. Class-codes were obtained from the background reading and citation check of few relevant patents and from different other databases like USPTO, WIPO and Espacenet. Class-codes related to drilling of boreholes and well development was taken into consideration. Comprehensive search strategy was made using the combination of different keywords and complimentary class-codes in order to obtain all the relevant patents and at the same time keep away from irrelevant records.
Process-flow for patent analysis
Database used: Thomson Innovation
Countries Covered: US Grant, GB App, US App, FR App, WO App, DE Util, EP Grant, DE Grant, EP App, DE App, JP Util, JP Grant, JP App, CN Util, CN App, KR Util , KR Grant, KR App, DWPI
Years searched: Priority date: 1990-01-01 to 2011-12-22
Date of search: 22nd December 2011
Keywords: The keywords used for different concepts are
- Tight Gas: Tight gas, tight sand, tight carbonate, tight formation, tight deposit, tight strata, tight medium, impermeable formation, impermeable deposit, impermeable strata, impermeable medium, impermeable reservoir etc.
- Stimulation: Stimulation, fracturing etc.