USE OF DRILL CUTTINGS AS A FLUID-TIGHT MEMBRANE AND METHOD FOR ESTABLISHING SUCH MEMBRANE.
The present invention relates to use of drill cuttings in order to provide a fluid tight membrane or a sealing layer in a structure. More particularly, the present invention relates to use of drill cuttings, formed as waste product from for example drilling of wells in oil and gas industry, to form a fluid tight layer or a membrane. The objective of the invention is to provide an industrial application of the waste product named drill cuttings, resulting from drilling wells. When drilling wells for exploration and/or production of, for example oil and gas, large quantities of waste products in the form drill cuttings are produced. Drill cuttings comprise clay, sand and crushed rock. . Drill cutting may generally be defined into two main groups; drill cuttings forced to the surface by application of a water based drill fluid, referred to as water based drill fluid below; and drill cuttings forced to the surface by using a drill fluid containing inter alia a petroleum compound, referred to as oil based drill cutting below. To-day water based drill fluids are to a large extent preferred in lieu of oil based drill fluids, provided this is technically acceptable. One major reason for preferring water based drill fluids is that drill cuttings forced to the surface using water based drill fluid are allowed to be deposited around the drill well, for example on the sea bed. In certain environmentally vulnerable areas, however, it is not allowed to deposit any drill cuttings of any type around the well opening, for example on the sea bed. Consequently, all drill cuttings produced during drilling of wells in such areas must be transported to approved deposit sites onshore, thus representing a deposit problem. There is a need for and a requirement of utilizing the drill cuttings as raw material for other industrial purposes, subsequent to required separation and possible re-use of oil containing drill fluids and other substances from drill cuttings transported ashore from for example drilling of wells offshore. In such way the drill cuttings may completely or partially substitute other resources . Hence, the drill cuttings constitute a resource instead of being a waste product to be deposited onshore. Additio¬ nally, other resources are saved and transport and mass transfer are reduced, giving a substantial environmental improvement. Drill cuttings consist of masses of well graded particle sizes and may contain relatively large portions of clay, expanding when brought into contact with water. This material property makes drill cuttings suitable for formation of a fluid tight layer which completely or partly may substitute tightening seals which traditionally are produced using fabricated membrane sheets or layer of for example bentonite pellets . In the following, use of the term "drill cuttings", shall mean drill cuttings which, by applying any known technology, are sufficiently cleaned and rinsed for any detrimental chemical compounds, such as for example drill cuttings containing petroleum products. The term "drill cuttings" also means drill cuttings mixed with a portion of sand. This may be done in order to improve the properties of drill cuttings during handling and laying; and in order to increase the load carrying capacity, provided that the expansion and/or sealing properties still satisfy the requisite requirements. According to one aspect of the invention drill cuttings are used as a fluid tight layer or membrane in a structure. One example of a structure wherein drill cuttings, based on in situ tests, have proved to be function satisfactory as a fluid tight layer or membrane, is in connection with anaerobic breakdown of organic materials. In such structure the organic materials are encompassed by a fluid tight membrane, made of drill cuttings. Such structure will be denoted as "methane gas cell". According to one preferred embodiment the methane gas cell comprises a top part made solely of drill cuttings. According to a second embodiment at least parts of the bottom portion and side portions of the methane gas cell are made solely of drill cuttings. According to the most preferred embodiment the bottom, top and side parts of the methane gas cell are made solely of drill cuttings. When the organic material within the methane gas cell is broken down in an anaerobic manner, methane gas is formed. Said gas is transported out of the cell in a known manner through a pipe system and may be used as a source for production of energy. A second aspect of the invention relates to a method for providing a fluid tight membrane by utilizing drill cuttings, comprising the following steps: - providing a bottom surface upon which the membrane shall be arranged; - placing a layer of drill cuttings; and - compacting the layer of drill cuttings . Dependent upon the content of water and/or degree of moisture in the drill cuttings, it may be necessary to add water to the drill cuttings in order to obtain sufficient expansion of the clay particles in the drill cuttings. This is particularly relevant for dry cuttings obtained from cleaned oil based drill cuttings. A method for producing an encapsulation, which in the following is denoted methane gas cell, utilizing a membrane made of drill cuttings, incorporates the following steps: - providing a surface for supporting the bottom part of the methane gas cell; - placing a layer of drill cuttings on the surface, the layer forming the bottom part of the methane gas cell; - compacting the layer of drill cuttings; - placing a rim layer of drill cuttings along the periphery of the bottom part; - compacting the rim layer of drill cuttings placed along the periphery of the bottom part; - placing a layer of porous material on top of the drill cuttings, intended to house the material to be broken down; - placing a layer of drill cuttings on top, the layer forming the entire or part of the sealing top part of the methane gas cell; - compacting the top part, - providing at least one fluid communication duct between the porous material layer and the exterior of the methane gas cell; - feeding the material to be broken down into the porous material layer; and - making provisions for transporting out gasses formed within the encapsulation. According to an alternative method for constructing a methane gas cell the organic material is introduced into the porous material layer prior to placing the top part on top of the porous material layer and the organic material. The porous material layer may be made of any material suitable to provide a porous layer having cavities suitable for containing the organic material. According to a preferred embodiment the porous layer is made of wooden chips which will be broken down together with the supplied organic waste material. A typical organic material to be deposited in a methane gas cell may be waste products from for example, but not limited to, waste from the fish industry. Another example may be wasted food or waste from food and nutrient industry, such as waste from slaughterhouses or the like. The present invention, and in particular use of drill cuttings, is particularly, but not exclusively suitable for use in connection with areas where natural geology do not have sufficiently low permeability and in connection with solutions requiring enhanced barriers, provided in an artificial manner. In the following a non-limiting embodiment of application of the invention is disclosed, illustrated by the accompanying drawings, wherein: Figure 1 shows a section through a methane gas cell shown in perspective, the methane gas cell being placed on a soil surface and being encompassed by a membrane made from drill cuttings; Figure 2 shows a second embodiment of a methane gas cell, equipped with an outlet duct for exhaust gas and an inlet duct for supply or feeding of organic materials for anaerobic breakdown; Figure 3 shows drill cuttings used to enhance the geological barrier, the drill cutting forming a part of a bottom liner in a deposit, placed in a hole in the ground; Figure 4 shows a complete bottom liner wherein drill cuttings are used to enhance the geological barrier. The drain system between the geological barrier and an artificial barrier is not required, but improve the safety measures against leakage; Figure 5 shows a deposit, partly filled with waste, wherein the produced gas is vented out of the waste materials; Figure 6 shows a completed deposit with a top layer in which a fluid tight membrane of drill cuttings is incorporated; and Figure 7 shows an alternative embodiment wherein a biocell is established inside a deposit in order to improve the safety. In the Figures the reference number 1 denotes a methane gas cell, comprising a bottom membrane 3, side membranes 5 and a top membrane 7, all being made of drill cuttings from drilled wells and encompassing a porous part 9, providing cavities for introduction of organic material 9' into the cell 1 for anaerobic breakdown. In Figure 1 the boundary of the side membrane is indicated by dotted lines. For the sake of clarity the sectioned area through the membrane 3,5,7 is not shaded and the dimensional proportions between the porous portion 9 containing the organic material 9' and the surrounding membranes 3,5,7 may also differ from the shown proportions. During anaerobic breakdown of organic material 9' methane gas is inter alia formed, such gas being vented from the cell through any known venting system (not shown in Figure 1) . The venting system is connected to a plant (not shown) , exploiting the methane gas for production of energy in any known manner. As shown, the side membrane 5 forms an angle (V) with respect to the horizontal plane, the angle (V) being approximately 30°. Angles greater than approximately 45° are not desirable, since the process of achieving sufficient compacting of the drill cutting may become difficult. Figure 2 shows a variant of a methane gas cell 1, comprising a bottom part 3, side walls 5 and a top part 7. The shown variant may for example be a variant wherein the cell 1 is constructed in an excavated hole in the ground (not shown) . The cell contains a porous fibre material, for example in the form of wooden chips. Further, Figure 2 shows a cell 1 provided with an exhaust pipe for methane, one end of which being placed inside the cell 1, connected to a pipe system 4 equipped with a number of apertures 10. The apertures 10 are in open communication with the cavities of the cell 1. The cell 1 is further provided with a fluid communication duct β. The end of the duct 6, arranged inside the cell 1, is connected to a pipe system 8 equipped with a number of openings 11, intended to feed biological material into the cell. For such solution it is possible to feed new biological material to or pump out previously introduced biological material, completely broken down. The pipe system 4 for methane may preferably be arranged in the upper part of the cell, while the pipe system 8 for supply of new biological material may preferably be arranged near the bottom of the cell. Figure 3 shows in perspective a vertical section through an empty deposit 1. The deposit 1 is excavated or blasted out in the ground 12 and at its lower end it is provided with a reinforcement of the geological barrier in the form of drill cuttings. The layer 15 of drill cuttings is a supplement to the inherent geological barrier formed by the ground. Drill cuttings may be used alone or mixed with sand, dependent upon the inherent properties of the actual drill cuttings . Figure 4 shows in perspective a vertical section through a variant of an empty deposit. The Figure shows a complete bottom liner comprising a lower layer 15 of drill cuttings, a layer 14 of gravel, an artificial membrane 16 of a suitable material, and an upper layer 17 of gravel. The liner 13 according to this embodiment is equipped with a drain pipe 18 for leakage control and a drain pipe 19 for collecting leachate. The drain pipe 18 for leakage control is placed in the lower layer 14 of gravel, while the drain pipe 19 for collection of leachate is placed in the upper layer 17 of gravel. The layer 15 of drill cuttings represents a supplement barrier to the natural geological barrier of the ground. Figure 5 shows the deposit in Figure 4 at a later stage where also the pipes 4 for collecting methane via a manifold 20 is connected to a methane station for production for example of electricity, hot water for heating or direct delivery of methane for industrial application. Figure 6 shows the deposit completely filled with a waste material, where the deposit at its upper end is equipped with a top sealing 7 where drill cuttings are incorporated as a fluid tight membrane. At its lower end the deposit is sealed by means of a bottom liner 13 as described above. Figure 7 shows the same deposit as shown in Figure 6, the deposit being in addition provided with an additional, separate biocell 22, equipped with a schematically illustrated pipe arrangement 23 for filling/emptying organic waste material; for controlling the breakdown process; and for withdrawal of methane gas. In principle, the pipe arrangement may be as shown in Figure 2. The bottom and the top of the biocell 22 may preferably be formed of drill cuttings. This deposit may optionally be incorporated into a plant (not shown) for post maturing of organic broken down waste from the biocell 22. Such solution placing the biocell inside a deposit, will increase the safety associated with biocells, since a possible leakage from the biocell or spillage/accidents associated with feeding and discharging material from the biocell will be controlled by the leachate system of the deposit. As described above the invention represents a substantial environmental improvement, since use of drill cuttings, which traditionally are considered to be a waste product, is according to the invention industrially used as a substitute material instead of industrially produced material. The new use of drill cuttings is thus an important contribution for reduction of the volume of waste caused directly or indirectly as a result of well drill activities. The term "bottom liner" means the main bottom of the deposit and includes the side walls of deposit .
