AU2015200036A1 - Method of Sealing Pores and Fractures Inside Boreholes With Biodegradable Micronised Cellulose Fibers and Apparatus for Making the Micronised Cellulose Fibers - Google Patents

Abstract

Abstract A method of testing the effectiveness of a sealant for sealing pores and fractures inside a borehole comprises the steps of: mixing the sealant with a drilling fluid; placing a material that the sealant is to seal in a vessel; placing the sealant and 5 drilling fluid mixture in the vessel; applying pressure to the mixture; and determining if there has been any loss of fluid from the mixture through the material.

Description

1 METHOD OF SEALING PORES AND FRACTURES INSIDE BOREHOLES WITH BIODEGRADABLE MICRONISED CELLULOSE FIBERS, APPARATUS FOR MAKING THE MICRONISED CELLULOSE FIBERS, AND TESTING METHOD 5 Field of The Invention This invention is related to a method of sealing pores and fractures inside boreholes with a biodegradable product. Particularly this invention concerns the application in the oil, gas and geothermal drilling as an additive to the drilling 10 mud system by which the micronized organic cellulose fibers are added into the drilling mud system and that will form a thin and strong wall cake inside the borehole. The invention is not limited to the process of developing micronized cellulose fiber materials but also in the apparatus itself that will produce such specialized sealant for the oil, gas and geothermal industry. In addition, the 15 apparatus is related to a method of testing the effectiveness of a sealant for sealing pores and fractures inside boreholes. Background of the Invention Drilling for oil, gas or geothermal wells usually occurs in a depth of thousands of 20 meters. In order to form the borehole, cutting needs to be diverted to the surface and circulating drilling mud through a drill pipe. Various additives are mixed to maintain a consistency property of the drilling mud so that it can carry cutting to the surface which in turn keeps the borehole stable. Problems that can occur while drilling include things such as "lost circulation" (i.e. drilling mud is lost within the 25 fractures of the borehole), increase of "torque" where the drill pipe is rotating and "drag" occurs while drill pipe moves up or down. Other associated problems with an unstable borehole are sloughing of formation (e.g. coal, shale, differential sticking where the drill pipe is stuck while drilling. These problems are commonly occur while drilling oil, gas and geothermal wells but most importantly the cost 30 incurred can add up to millions of dollars furthermore if there is a well blow out than the damage can be fatal to those near the site. In the past, the common practice to combat these associated problems was the addition of grounded coconut shell, ground-up formica or other inorganic fibers. All of these supplements could not inherently solve the various drilling problems especially with the lost 2 circulation yet instead it might had further damage if it happened during the producing formation zone where it plugged the pores irreversibly. The addition of particles/solids that can penetrate the formation by virtue of being non biodegradable, may obstruct the producing zone thus making the well none 5 productive. There have been other organic products developed from rice husks, peanut shells and other type of softwood however these products have some disadvantages in their application as drilling fluid additives due it its natural properties. 10 The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application. 15 Summary of the Invention It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the 20 consumer with a useful or commercial choice. Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the 25 present invention is disclosed. A preferred objective of the present invention is to overcome operational problems related to drilling wells, which means cost effective drilling. 30 It is another preferred objective of the present invention to provide a mechanism for the process of achieving a very effective sealant.

3 It is a further preferred objective of the present invention to provide a method of testing the effectiveness of a sealant for sealing pores and fractures inside boreholes. 5 According to a first broad aspect of the present invention there is provided a method of sealing pores and fractures inside a borehole, the method comprising the steps of: providing a sealant of biodegradable organic cellulose fibers 10 including fibers of ground up teakwood; and mixing the sealant with a drilling fluid; and pumping the sealant and drilling fluid mixture down the borehole to 15 seal the borehole pores and fractures. The invention provides a method of sealing pores and fractures inside a borehole, as possibly one of the many additives to the drilling mud/fluid system. Since the additives are fibrous and inert they will mechanically form an impervious layer in 20 order to enhance the wall cake by being strong yet remaining thin. Preferably, the particular type of organic cellulose fiber being used is fibers of ground up and sized teakwood which can be blended with sized cotton. It is preferred that the blend of these two types of cellulose fibers can vary from 80% 25 20% to 60% : 40% with the predominant percentage being teakwood. Preferably, the fibers of ground up teakwood will have particle sizes varying from mesh 40 to mesh 325, and the particular optimum particle size range is preferably mesh 60 to mesh 325 with a preference of mesh 80 to mesh 325. 30 Preferably, the ground up cotton fibers will have a range of particle size from mesh 10 to mesh 40 with preference range of mesh 10 to mesh 20.

4 According to a second broad aspect of the present invention there is provided a method of testing the effectiveness of a sealant for sealing pores and fractures inside a borehole, the method comprising the steps of: 5 mixing the sealant with a drilling fluid; placing a material that the sealant is to seal in a vessel; placing the sealant and drilling fluid mixture in the vessel; 10 applying pressure to the mixture; and determining if there has been any loss of fluid from the mixture through the material. 15 Preferably, the drilling fluid comprises hydrated clay. It is preferred that the clay comprises bentonite. Preferably, the method also comprises the step of preparing the clay be pre 20 hydrating it. It is preferred that 350ml of the pre-hydrated clay is prepared. Preferably, 10ppb (lbs per barrel) of sealant is mixed with the drilling fluid. Preferably, the sealant comprises ground-up cellulose fiber. 25 Preferably, the vessel comprises an American Petroleum Institute (API) cylinder cell. Preferably, the material is placed in the vessel without any filter paper. 30 Preferably, the material comprises sand. It is preferred that the sand comprises gravel pack sand. It is preferred that the gravel pack sand comprises 20/40 gravel pack sand.

5 Preferably, the step of placing the material in the vessel comprises filling about one-third of the vessel with the material. Preferably, the step of placing the mixture in the vessel comprises pouring the 5 mixture into the vessel. Preferably, pressure up to 100psi is applied to the mixture. Preferably, the step of determining if there has been any loss of fluid from the 10 mixture through the material comprises determining if any fluid from the mixture comes out of the vessel. Preferably, the step of determining if there has been any loss of fluid from the mixture through the material comprises determining if there has been any loss of 15 fluid from the mixture within a predetermined period of time following the application of pressure to the mixture. It is preferred that the predetermined period of time is 10 minutes. Detailed Description of the Invention 20 In the process of drilling for oil, or geothermal wells, especially the two latter activities, lost circulation is very common and if not handled properly various problems will occur. If the formation contains gas then the drilling fluid that occupies the borehole column can enter the fracture formation and gas in turn will 25 surface which could trigger a major explosion if a spark results due to metal and steel hitting one another. Moreover, any delays due to problems while drilling oil, gas, or geothermal wells always results in financial losses. Thus in order to achieve affiance in drilling these wells prevention is the best method, however there have already been numerous attempts by adding additives that do not 30 particularly solve these problems, and in fact they damage the formation zone making the wells non-productive. The invention of ground up and sized cellulose fiber, from teakwood has resulted in the most effective method in minimizing problems related to the drilling mud system. The ultimate additive that effectively prevent lost circulation, reduce torque and drag, prevent sloughing of coal and 6 various shales, should not damage formations and yet be biodegradable. Hence, this is the purpose of the invention. Furthermore, the invention provides a method to seal pores and fractures inside 5 boreholes with a biodegradable sealant, which involves the following steps: a. To provide sufficient supply of raw materials so that the finished sealant can be created in the right mixture. b. To mix a certain ratio of sealants with drilling mud, and then to pump continuously the drilling mud that is already mixed with the sealant so 10 that it adheres tightly and completely covers all pores and fractures at the wall of the borehole, thus no more fluid losses and drilling mud in the borehole column is stabilized. The above method is using a sealant that is derived from an organic cellulose fiber 15 therefore it is naturally biodegradable. The organic fiber is made from teakwood that is ground up and sized or it can also be blended with sized cotton. In accordance with the invention, selection and research of the type of wood was confined to hardwood and having tried various types of hardwood, teakwood was found to have optimum properties for an effective sealant. Its natural properties 20 fits all the criteria required as an effective sealant and being organic in its nature, hence environmentally friendly. The teakwood when ground up to a fine fibrous particles along with the above mentioned mesh sizes, when mix in the drilling fluid system and pump downhole, under the hydrostatic pressure will form a matrix in the wall cake thus making the wall cake strong yet it remains thin. This so called 25 "thin and strong wall cake" will make the borehole stable and will ultimately minimize various drilling problems associated with unstable drilling fluid properties. The most significant effect is the mechanical function of inhibiting fluid loss into the formation of the borehole which is the main cause for various problems occurring while drilling oil, gas, or geothermal wells. Another advantage 30 of the fibrous particle is that it will not penetrate the formation and will not plug or damage the formation because the "matting effect" created by the fibrous particles is only at the surface of the borehole.

7 We have also developed a method of testing which can determine the effectiveness of the sealing capability of a particular additive and also observe the "matting effect" of the fibrous particle on the wall cake. Other types of organic cellulose fibers that were tested were Meranti wood, Albacia wood, Mahony wood and Pine 5 wood, where eventually Teak wood had the best result of having the thinnest wall cake and yet no fluid loss observed after 5 minutes of 100 psi pressure applied. The method of testing designed is as follows: 1. Prepare 350ml of pre-hydrated bentonite. 10 2. Mix 10ppb (lb per barrel) of ground up cellulose fiber with prepared bentonite. 3. Fill the API cylinder cell (without any filter paper) with 20/40 gravel pack sand to about 1/3 of the cylinder. 4. Pour the mixed cellulose fiber or bentonite into the cylinder. 15 5. After the cylinder is closed then apply pressure to 100 psi. 6. If within 10 minutes there is no spurt or fluid loss then it can be concluded that the particular cellulose fiber can effectively sealed the pores of the sand based formation, if drops of fluids comes out of the bottom of the cylindrical cell, then the particular fiber failed to form an 20 effective matting to seal the most permeable pores. Various tests conducted with regards to the above method were the main criteria in selecting and optimizing a particular grounded wood as the most effective additive to perform the sealing ability of the most permeable formation. 25 It was concluded that Teak wood ground up to a particle size ranging from mesh 40-325 was an effective range, but there is still a preference of mesh 60-325 for certain application and the most effective and optimum range is mesh 80-325. The range size can be modified to suit a particular application. 30 To seal large pores or "vulgar formation" the ground up teak wood is blended with ground up cotton fibers with a ratio of 80:20 up to 60:40 the latter no. being the grounded cotton fibers. If the pores are bigger than the "vulgar formation" or the so called "cavernous formation" then "pill" of drilling mud can be added with 8 ground up and sized Calcium Carbonate or Salt on top of the already mixed ground up cellulose fiber. Having studied various drilling problems as well as numerous additives, our 5 invention has a specific approach where it basically overcomes various problems such as miscibility in the drilling fluid system, sealing ability in the various downhole formations, or forming an effective thin wall in cake in the borehole, as well as being biodegradable means that it is environmentally friendly. The use of a specific type of ground up hardwood (tectora grandis) combined with sized cotton 10 (gossipium) is found to be the optimum combination in forming a sealant to prevent damage to the formation zone while combating the problems of lost circulation effectively. It is an ideal additive because it is stable and inert (it does not have any reaction such that it can change the properties of the drilling fluid/mud). Also the fact that 15 it's fibrous means it will not penetrate the pores of the borehole. This of course is non-damaging to the formation and environmentally friendly because it is biodegradable. The manufacturing process of ground up teak wood as a drilling fluid additive 20 involve the following steps: a. Obtaining teakwood in the form of chips before grounding process. b. Micronising teakwood chips by grounding and sizing c. Optimising particle sizes to a range of mesh 40-325. 25 In accordance with the invention, the teakwood used has the same mesh. Therefore an apparatus/mechanism is needed for producing the same particle of teakwood and it is as follows: 1. The "Hammer Mill" which involves an impact of hammer against the wall of the mill. The "Disc Mill" which involves spinning of two discs, the 30 process is where the wood chips are ground up to fine particles. 2. The "Hydrocyclone" is the sizing of the already ground up teakwood, where speed is adjusted to obtain the required particle range.

9 Modifying the invention can be made without any deviation from the scope plus effectiveness of the invention in producing the particular organic cellulose fiber for the purpose of drilling fluid additive. Throughout the specification and claims, unless the context requires otherwise, the 5 word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Throughout the specification and claims, unless the context requires otherwise, the term "substantially" or "about" will be understood to not be limited to the value for 10 the range qualified by the terms.

Claims (18)

1. A method of testing the effectiveness of a sealant for sealing pores and fractures inside a borehole, the method comprising the steps of: mixing the sealant with a drilling fluid; 5 placing a material that the sealant is to seal in a vessel; placing the sealant and drilling fluid mixture in the vessel; applying pressure to the mixture; and determining if there has been any loss of fluid from the mixture through the material. 10

2. The method defined by claim 1, wherein the drilling fluid comprises hydrated clay.

3. The method defined by claim 2, wherein the clay comprises bentonite.

4. The method defined by any one of claims 2 to 3, wherein the method also comprises the step of preparing the clay by pre-hydrating it. 15

5. The method defined by claim 4, wherein 350ml of the pre-hydrated clay is prepared.

6. The method defined by any one of claims 1 to 5, wherein 10ppb (lbs per barrel) of sealant is mixed with the drilling fluid.

7. The method defined by any one of claims 1 to 6, wherein the sealant comprises 20 ground-up cellulose fiber. 11

8. The method defined by any one of claims 1 to 7, wherein the vessel comprises an American Petroleum Institute (API) cylinder cell.

9. The method defined by any one of claims 1 to 8, wherein the material is placed in the vessel without any filter paper. 5

10. The method defined by any one of claims 1 to 9, wherein the material comprises sand.

11. The method defined by claim 10, wherein the sand comprises gravel pack sand.

12. The method defined by claim 11, wherein the gravel pack sand comprises 10 20/40 gravel pack sand.

13. The method defined by any one of claims 1 to 12, wherein the step of placing the material in the vessel comprises filling about one-third of the vessel with the material.

14. The method defined by any one of claims 1 to 13, wherein the step of placing 15 the mixture in the vessel comprises pouring the mixture into the vessel.

15. The method defined by any one of claims 1 to 14, wherein pressure up to 100psi is applied to the mixture.

16. The method defined by any one of claims 1 to 15, wherein the step of determining if there has been any loss of fluid from the mixture through the 20 material comprises determining if any fluid from the mixture comes out of the vessel.

17. The method defined by any one of claims 1 to 16, wherein the step of determining if there has been any loss of fluid from the mixture through the material comprises determining if there is has been any loss of fluid from the 25 mixture within a predetermined period of time following the application of pressure to the mixture. 12

18. The method defined by claim 17, wherein the predetermined period of time is 10 minutes.