Water absorption technology of gas drilling
Tang Bo1,a,Feng Guangtong 1,b and Xu Hao 1, c
1Drilling
Technology Research Institute, Shengli Petroleum Administration
Bureau, SINOPEC.
No. 827, Northern Road #1, Dongying City, Shandong Prov. 257017, China.
atangbo2004@126.com,bfengguangtong.slyt@sinopec.com,
cxuhaoswpi@yahoo.com.cn
Keyword: Gas drilling, Formation water, Super-absorbed material, Water
carrying
Abstract: In recent years, the development of super-absorbent material was very fast,
its ability to absorb water up to several hundred or even thousands times of its own
weight, it provides a new way of gas drilling to solve the water carry problem.
According to the characteristic of the formation, we optimized polyacrylic acid salt as
the water absorbent material, and evaluate salt resistance, temperature resistance and
compression resistance. And we discussed the feasibility and recycling of the
technology. And we find that this kind of super-absorbent material which can absorb
deionized water 1484 times，absorb 0.9% NaCl aqueous solution 687 times，absorb 50%
ethanol 705 times, that can meet the water carrying requirements of gas drilling.
1 Introduction
Gas drilling technology is a kind of underbalance drilling technology which uses air,
natural gas or nitrogen as circulation medium to. Compared with the conventional
drilling technology, its advantage is fast ROP, small reservoir damage, eliminating
loss and overcoming wall collapse caused by water out. Because of water out,
application of gas drilling technology is limited. If gas drilling meets water out, it
must convert the conventional drilling technology used drilling mud.
Super absorbent polymer refers to as SAP, and it is also known as high absorbent resin
and super water absorption, and it is new functional polymer material which has the
ability of excellent water absorption and water retention. The water absorbing
capacity of some kinds of synthetic solid absorbent material can be thousands of their
original quantity. There is no free water on the surface of it, so its water absorption,
water absorbing speed and water retention are very strong. And it is popular with
medical and health supplies(such as slow release drugs, antithrombotic materials, etc),
daily water absorbing materials (such as diapers, sanitary towels, etc.), soil
improvement material and industrial water plugging water absorption. And it is used
as water plugging material in petroleum industry. Because of its high water absorbing
capacity, it provides a new way of gas drilling to solve the water carry problem.
2 Super absorbent polymer of gas drilling
To study the feasibility which the super absorbent polymer is used in gas drilling, the
researchers made tests to optimize the super absorbent polymer to make sure the
modified method and component, and value the characteristic of the material. The
super absorbent polymer which was composed balanced absorbing water speed,
absorbing water quantity and geltxh
strength. And the water absorbing capacity of
the super absorbent polymer is no less than 300 times under 70℃， and the water
retention rate is more than 70% under the pressure of 5MPa, and the saline water
absorbing capacity is no less than 120g/g.
3 Technique
The feasibility of super absorbent polymer mainly includes two aspects: one is the
ground equipment, and the other is the through capacity of the borehole. The super
absorbent polymer is usually in the form of powder, and the ground equipment of gas
drilling technology should be increased a set of high pressure injection equipment.
And SAP material can easily go through the hole of the drill string, and then SAP
absorbs water and carry cuttings when it return to the surface. And the density of SAP
is smaller than the cuttings(about 2.5~3.0g/cm3), so it can be easily carried to the
surface. There is no free water on the surface of it, so its water absorption, water
absorbing speed and water retention are very strong, so it can make the wall of hole
dry.
4 Recycling method
The volume of the polyacrylic acid salt super absorbent material expands after it
absorbs water, and is held in the state of suspension. And SAP material can easily go
through the hole of the drill string, and then SAP absorbs water and carries cuttings
when it returns to the surface. And how it can be separated is a problem.
Through researching, we design a separating method which is suitable with gas
drilling technology. And the SAP recycling process is shown as below:
a. SAP absorbs water and carries cuttings when it returns to the surface, and then
enters the sand collector, and cuttings sinks, and SAP suspends.
b. SAP which suspends is discharged into the separation pool, and there is a filter in
the separation pool. The water which is filtered is absorbed into the sand collector,
and SAP material which is absorbed can be separated from the cuttings.
c. Plenty of salt is filled into the sand collector to avoid SAP continuing absorbing
water.
5 conclusions
Gas drilling technology have very distinct advantages, it can improve ROP greatly,
shorten the drilling cycle, reduce drilling costs, but it's scope of application was
greatly limited by the problems of formation water and wellbore stability. This project
developed a kind of super-absorbent material which can absorb deionized water 1484
times，absorb 0.9% NaCl aqueous solution 687 times，absorb 50% ethanol 705 times,
that can meet the water carrying requirements of gas drilling. It provides a new way of
gas drilling to solve the water carry problem.
Acknowledge
This work was financially supported by the Sinopec prospective subject.
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