Basins, Tight Sand, & Shale Plays, Oh My! (Part 2)Posted on November 28, 2014 by Amy Jerina
Last week we discussed what a Basin is and how the word is used in the oil and gas industry. I used the same map below last week, since it perfectly illustrates the locations of all the basins, tight sands, and shale plays that are located within the United States of America. If you did not read last week's blog be sure to check it out- it talks about basins!.
I have read numerous articles from industry resources- it seems that "Tight Sand" is not the only way to refer to tight Sands. You can say: Tight Sand, Tight Gas, Tight Gas Reservoir, or even Tight Gas Sands were all thrown around in the different articles.
The term I am going to use throughout this article is "Tight Sand." However, Tight Sand does not have a formal definition, which drives me crazy. The definitions vary as much as the phrase is used. I am going to do my best to compile all the different definitions make sure we all have some kind of understanding. Bear with me my friends.
What is Tight Sand?
Tight Sand refers to low permeability sandstone reservoir that produces primarily dry natural gas. A tight gas reservoir is one that cannot be produced at an economic flow rate or recover economic volumes of oil and gas without massive assistance from large stimulation treatments of any special recovery process.
The above definition is the most agreed upon from all the research I have done. If you understand that definition outright, you get a gold star. I,however, need it broken down a bit more.
- Low permeability is when it takes A LOT of pressure to squeeze fluid through a rock.
- Sandstone is a sedimentary rock found mainly in basins. It often serves as an aquifer for ground water, or in our case. reservoir for oil and natural gas.
- We know dry gas is almost pure methane, with very few hydrocarbons.
- An economical flow rate is a flow rate that is profitable and a profitable volume
- Stimulation treatments would be steam injection, hydraulic fracturing or horizontal wellbore
So, now that I have figured out that "tight gas" is what is extracted from "tight sand", and is considered to be an unconventional resource, since it incorporates the new ways of drilling, or extracting from the ground. The gas is found in a formation that is very old, over 240 million years to be more exact. Over the millions of years, the rock formations have been compacted and undergone cementation to reduce its permeability. Of course, there is no such thing as a typical tight gas reservoir. What fun would that be?! They can be deep or shallow, high pressure or low pressure, high temperature or low temperature, single layered, multi-layered, you get the idea. It seems that the main problem with these geological formations is trying to figure out if the risk of drilling is worth the reward of the gas.
The map below shows the major tight gas sand basins here in the United States. Its a little easier to see the definition than the above map. Obviously, they are located in the same area as the basins because they are part of the basin, but just a different geological formation within the basin. The tight sand covers a much smaller area than an entire basin.
The figure below is called a 'resource triangle' It is a concept to explain how all natural resources are distributed in nature. If you are prospecting for natural gas or any natural resource for that matter, you will find that the best high-grade deposits are small in size and, once found, are easy to extract. The hard part is finding a pure vein to these high permeability gas fields. The deeper into the triangle, the lower grade the resource, but the larger the quantity. The deeper we go, the better the technology needs to be for drilling and processing the natural resources.
Tight Gas that comes from the tight sandstone within basins is just another natural resource that the United States is utilizing. There are still volumes the gas within the tight sand reservoir that have been discovered, but we have just have not gotten to it yet. And I stress yet. The proof to that: The United States has been producing tight gas for more than four decades, and now it accounts for approximately 40% of the nations unconventional gas output. If you want to learn more about natural gas is processed you can read about that here.
Amy Jerina is an Account Representative with Croft Production Systems which is located in Needville, Texas. At Croft she focuses on growing existing customer relationships & helps to develop new client prospects. With a focus on increasing sales of the organization’s products & services. Amy also works with the marketing & business development team members in the office to ensure CROFT is meeting its client needs. She collaborates with field representatives & engineers as a liaison between the company & clients. Amy provides unlimited support to customers over the phone & is able to conduct field visits with clients located in the Continental United States. Amy has over 10 years of management, training & sales experience & over 15 years of customer service skills. She is using this experience to break into the oil & gas industry. By writing this weekly blog Amy is growing her oil & gas knowledge and hope to share that knowledge with anyone who wants to learn.