Hydraulic Fracturing in Oil and Gas Well Reservoir - Term Paper Example

Contents Contents 2 Hydraulic Fracturing Process Report 3 1.0.History of hydraulic fracturing 3 2.0.Importance of hydraulic fracturing 4 3.0.Hydraulic fracturing process 5 4.0.Hydraulic fracturing equipment 7 5.0.Hydraulic fracturing fluid and additives 8 6.How deep the fracture 9 7.References 11 Name: Unit: Number: Course: Supervisor: Submission date: Hydraulic Fracturing Process Report 1.0. History of hydraulic fracturing Gas and oil are seeps which occur naturally as hydrocarbon, flow and collect on the surface. Early exploration of gas and oils looked into finding the conventional reservoirs that allowed the hydrocarbons to flow naturally and with ease to the surface. Prolonged period of oil and gas exploration has forced new discoveries of pressure form of simulation to provide sufficient hydrocarbon as the conventional reservoirs got depleted. This process of pressure application is referred to as the hydraulic fracturing (SUG, p4). Hydraulic fracturing is a process which has been employed in new and old existing unconventional reservoirs to extract oil and gas since 1930s using high pressure. Dow chemical industry was the first to practice application of hydraulic fracturing. This is because the company realized that application of sufficient down-hole fluid pressure did increase the permeability. This was possible because the process caused the existing rock to fracture and deform allowing effective acid simulation (Teleghani 2009, p1). The process was possible because hydraulic fracturing increase the surface area of the path that reaches the hydrocarbon wellbore enabling hydrocarbons and other fluids to flow with ease from the rock of formation, into the fracture and subsequently to the wellbore (API, 2009 p 15). In 1947 non-acid fracturing technique was first employed in Kansas at Hugoton gas well field with the main objective of comparing this new adventure with the acidization technology. Hydraulic fracturing is currently practiced to improve the production levels of gas and oil wells. In North America, since 1950, there has been several production wells drilled of which 50% and 70% oil and gas wells respectively were drilled using hydraulic fracture technique (Taleghani 2009, p1.) Hydraulic fracturing technique is also applied in geothermal energy extraction in addition to enhancing hydrocarbon production. Moreover, it is applied extensively for disposal of hazardous solid waste, ground water quifers, soil remediation, in mining industry for faulty reactivation and measurement of pressure resulting from in-situ materials. 2.0. Importance of hydraulic fracturing Hydraulic fracturing is of great significance to the national and domestic gas and oil requirement. This is because; this technique for over six decades has increased the catchment of hydrocarbons trapped within the unconventional reservoirs. Unlike conventional reservoirs unconventional reservoirs do not have the capacity to allow hydrocarbons flow. For conventional gas and oil reservoir they have interconnected pathways naturally within the matrix of the sedimentary rock. These pathways allow the gas and oil to easily flow and collect into the wellbore more often without any external pressure exerted or simulation. However, for unconventional reservorrs the rocks do have poor connected rock pores as well as smaller rock matrix grain that cannot allow ease flow of hydrocarbon. Moreover, unconventional reservoirs houses large quantities of hydrocarbons and hence, the hydraulic fracture technique is highly recognized and employed in the unconventional reservoirs to create or connect exitsing fractures so as to allow flow of hydrocarbons to the wellbore. This process, therefore, increase the quantity of hydrocarbon produced which in turn is able to meet the demand of energy (SUG p8-9). In addition, hydraulic fracturing technique allow for recovery of natural gas and oil from formations that once the geologist found it difficult to produce like tight shale formations. Hydraulic fracturing, in mature gas and oil fields it is used to prolong life of older wells (FracaFocus p1). 3.0. Hydraulic fracturing process Hydraulic fracturing technique is carried in stages. The stages are merely the same; however, the sequence is likely to change following the exhibiting condition of rock formation. In addition, additive composition (proportion and blend vary in reference to thickness, depth of a specific sites as well other existing rock characteristics (FracaFocus p.2). Stage 1: Perforation To kick start the fracturing process, a gun for perforating the well is lowered to the position of target. An electrical current which sets explosive form of charges is allowed down the well. The explosives shoots through the casing leaving behind holes through the casing of the well close to the shale formation. The holes are channels which allow hydrocarbon to flow to the wellbore as well as the fracturing fluid to move into the formation (Cabot, p2). Stage 2: An acid stage This stage involves passing thousands and thousands of a mixture of water gallons with a dilute acid like muriatic acid or hydrochloric acid at very high pressure (FracaFocus). The mixing is done at the surface (SUG, p13). The main aim of this mixture is to dissolve cement particles which might be in the wellbore. It also aims at providing open pathways for other fluids used in fracturing process by opening fractures close to the wellbore and by dissolving the mineral formed by carbonate (FracaFocus). Passing fluid into the formation at high pressure causes cracking. To achieve this, fracturing pressure ought to be more compared to the pressure produced by the geological forces onto the rock reservoir (SUG, p13). Stage 3: Pad stage This stage involves passing slick waters of about 100,000 gallons free of proppant material which then fills the wellbore, helps in opening of the formation and facilitates placement and flow of proppant material (FracaFocus). The fluids are passed at increased power rate. The extra power is determined by fluid pumping rate and the capacity of the fluid to ensure the cracks created are kept open hand in hand with the fracture growth (SUG, p.13). Stage 4: A prop sequence This stage may as well comprise of a number of sub-stages. The stage uses a mixture of water and proppant material. The proppant material may comprise of ceramic material or fine mesh sand, which is used to keep the created fractures open when the pressure is reduced (FracaFocus). To achieve this, the proppant material is deposited within the network of created fractures (SUG, p.13). In this stage, proppant material used varies in regards to size and amount. Water of several thousand gallons is also used (FracaFocus). Stage 5: flushing stage The excess proppant material present in the wellbore is flushed using large volumes of fresh water (FracaFocus) into the surface (SUG, p13). This stages is carried upon completion of treatment process (SUG, p13) 1.1. Perforating Perforating is the creation of holes using an electrical jet perforating gun through the casing of the well to the shale formation (Cabot, p.2). The perforating guns are well supplied with specialized shaped charges that are quite explosive. Then the shaped charge is released producing a very hot gas at high-pressure that vaporizes the cement, the pipes and the formation where it passes through. The outcome is tunnels like holes separated by the cement (API, p14). The holes created serve to allow natural gas and oil to flow into the wellbore and the fracturing fluid easily makes its way to the formation (Cabot, p2). 4.0. Hydraulic fracturing equipment The sophisticated process of hydraulic fracturing technique calls for several high tech-equipments and materials for vertical and horizontal well operations even for a short period of operation. The hydraulic fracturing equipments are designed such that they make it possible to drill several wells even within a single pad as well as undertaking hydraulic treatments. Where a thick reservoir is present in vertical wells as well as long horizontal wells, stimulation treatment are likely to be carried in different locations within a single well. This is referred to as multi-stage hydraulic fracturing perspective and as many as 150 fracture treatment can be performed a process which can go up to several months within one pad (SUG, p.16). The fracturing equipment houses multiple pumping units on its surface depending on the treatment(s) size, bigger sizes require high capacity pumping size, proppant material, adequate provision of fracture fluids, control units and blending units (SUG,p16). Proppant transport equipment, pumping equipment Fluid storage tanks and other ancillary equipment which includes manifolds, valves, piping and hoses. To ensure a successful treatment, companies which carry the process of hydraulic fracturing also provide a specialized control and monitoring equipment (API, p18). During the fracture process, series of data is collected from various units and conveyed to the monitoring equipment. Such data of great concern include chemical rate, sand concentration, slurry density, wellhead treatment pressure, rate of slurry delivery to the high-pressure-pumps, the rate of the fluid from the reservoir containers or tankers among others (APIp18). 5.0. Hydraulic fracturing fluid and additives Hydraulic fracture fluids differ in regards to the characteristics of a particular reservoir. The commonly used fluids are water based (SUG, p18) of which water and sand comprises of 99% fluid used and 1% or less comprises of chemicals (Cabot, p3).However, some types of rock reservoirs do have water sensitive clays which then call for usage of other types of fluids (SUG,p18). Regardless of the case of the rock, the fracture fluid either gas or liquid is passed into the reservoir at a high pressure so as to open the system of the fracture. Other fluids used in fracture process include the oil based fluids, propane, nitrogen, and carbon dioxide. Water is the basic fluid used in most cases of hydraulic fracturing. This is because it is cheap to obtain and it is readily available. For simulations that use water, water compatibility tests are carried before the onset of the fracturing process. Quantity of fracture fluid differs in reference to the number and size of treatment operations. For example a multi-stage treatment of a deep horizontal well can consume about 3500m3 to 15000m3 of water of which; where a single surface pad is being simulated for a shallow operations about 20m3 to 100m3 volume of water is commonly used. In summative form, the amount of water used for simulation can range from 0m3 to tens of thousands considering the nature of the geology and reservoir. Processes of fracture treatment are only carried once per zone and the process is completed ones the well’s productive life begins. Depending on reservoir or rock type the well can be in use for 7-30 years without calling for further water usage or treatment. In most cases water used for treatment are sourced from the nearby fresh water supplies, recycling recovered fluids and non-potable brackish water. These water alternatives, impacts on the water aquifers, water surface and lower water demand. To ensure continuous water supply to the treatment location water can be either piped or trucked to the site of the well and stored in either ponds or tanks (SUG, p 18). 5.2. Chemicals used in fracturing process Chemical used during the fracturing process are made to control bacteria, prevent corrosion and reduce friction (Cabot, p3). The chemical are added to the water to increase viscosity and ensure proppant materials are comfortably carried to the target area and back to the surface (SUG, p19).The chemical necessitates the ability to fracture the shale which would have been otherwise impossible without their application(Cabot, p3). The chemical used in the fracturing process must be in line with the federal and provincial regulations. 6. How deep the fracture Different factors determine how deep the fracture can be. For vertical drill the fracture extends up to where there is a ductile rock material. An example of a ductile material is the softer shale which does not fracture with ease as compared to brittle shale rocks. In such a case where the fracture meets a ductile rock forces, the fracture is likely to move within the brittle layers in horizontally. Lateral movement of the fracture will always continue so long as the pressure build by the fluid is greater than the pressure of the lowest stress within the fracture. In a lateral plane, the fracture can continue limitedly. However, this is prevented because: As much as the fracture can extend to over hundred meters the required fluid fracture pressure can increase beyond the pumping equipment capacity. Natural existing fractures can be channels for diversion of fracture fluid. The rock formation can be a target for fracture fluid dispersion. It is however, considerate that the depth of the fracture and amount of work performed be economically balanced to the production output accrued from the treatment. The proppant and fracture fluid used for each fracturing process will always vary in relation to the expected rates of production upon performing the treatment and the stresses from the tectonic reservoir rocks expected to be fractured (SUG, p14). The economical and production expectation versus work input is feasible using technology. This is because different computer software are available and are used to help in evaluating the best option before treatment takes place. In addition, both staff and the software do evaluate the parameters in place and carry out possible adjustment to ensure efficiency and safety of the work performed. Upon completion of a treatment, the different units are all compiled and analyzed in a computer software tool to help understand the stimulation results (SUG p15). 7. References API Guidance Document HFI First edition, (October 2009), Hydraulic Fracturing Operations-Well Construction and Integrity Guidelines Canadian Society for Unconventional Gas (SUG), Understanding Hydraulic Fracturing. Cabot Oil & Gas Exporation; Exploring the Hydraulic Fracturing Process FracaFocus Hydraulic Fracturing Process, retrieved from http://lookbeforeyoulease.files.wordpress.com/2011/10/introduction-to-hydraulic-fracturing.pdf, 27th February, 2014. Teleghani A. D., (2009), Analysis of Hydraulic Fracture Propagation in Fractured Reservoirs: An Improved Model for the Interaction between Induced and Natural Fractures, Texas University, Austin. Read More