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ISSN:2157-7463
Journal of Petroleum & Environmental Biotechnology

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The Influence of XC-Polymer on Drilling Fluid Filter Cake Properties and Formation Damage

Shafeeg O Blkoor* and Fattah KA
Petroleum and Natural Gas Engineering Department, College of Engineering, King Saud University, P.O. 800, Riyadh 11421, Saudi Arabia
Corresponding Author : Shafeeg O Blkoor
Petroleum and Natural Gas Engineering Department
College of Engineering, King Saud University
P.O. 800, Riyadh 11421, Saudi Arabia
Tel: 00966556202176
E-mail: [email protected]
Received September 13, 2013; Accepted October 14, 2013; Published October 21, 2013
Citation: Blkoor SO, Fattah KA (2013) The Influence of XC-Polymer on Drilling Fluid Filter Cake Properties and Formation Damage. J Phylogenetics Evol Biol 4:157. doi:10.4172/2157-7463.1000157
Copyright: © 2013 Blkoor SO, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The filter cake characterization is very essential for doing well selection of the drilling fluids that eliminates the drilling problems such as formation damage. A correct knowledge of filter cake properties gives petroleum engineers a tool for efficiently managing hydrocarbon production process of a field. This study aimed to experimentally investigate the effect of different concentration of XC-Polymer on filter cake properties, filtrate loss and formation damage to select the optimum concentration of the XC-Polymer. High Pressure-High Temperature (HPHT) filter press with ceramic disk device was used to conduct these experiments. Seven samples of water-based drilling were used in this study. The chemical compositions of the filter cake were described by using Scanning Electron Microscopy (SEM). The results show that the optimum concentration of the XC-Polymer in current study is 1.0 lb/bbl (1 g/ 350 ml); it was observed that 1g XC-Polymer per 350 ml of the drilling fluid is sufficient for appropriate optimum rheological efficiency. However, if more than 2 g. of XC-Polymer is added, the fluid loses its property and becomes almost immobile. Thus, at 1.0 g of the XC-Polymer concentration there is a less reduction in permeability of the ceramic disk. At this concentration, we got less reduction in permeability of ceramic disk and good properties of the filter cake. In addition, this is an indicator of less formation damage at this concentration of XC-Polymer.

Keywords
Drilling fluid; Mud cake; Formation damage; XC-Polymer
Introduction
Drilling fluids are the most critical parameter in the drilling operation and owing to the rapid development in the drilling well industry. It is very important to improve the properties of drilling fluids in order to satisfy the increasing demands. Mud can be described as thixotropicshear-thinning fluids with a yield stress [1]. The drilling fluids are originally designed in order to make sure that rotary drilling of subterranean formations is possible and economical. Furthermore, it is carrying cutting to surface, cooling and cleaning the bit, reducing friction, maintaining wellbore stability and preventing pore fluids from prematurely flowing into the wellbore. In addition, the drilling fluids are essentially designed to build a filter cake, which is basically intended to decrease filtrate loss to the formation, be thin and hold the drilling fluid in the wellbore [2].
One of the most critical functions of drilling fluids is to try to minimize the amount of drilling fluid filtrate entering the hydrocarbon bearing formation. The drilling fluid filtrates can lead to formation damage because of rock wettability changes, fines migration, drilling fluid solids plugging and formation water chemistry incompatibilities [3].
The filtration properties can be describes as one of the very important characteristics of all drilling fluids. The invasion of filtrate into the formation can substantially lead to reduction in the permeability of the near-wellbore region by a group of mechanisms: clay swelling, particles pore plugging, particles migration and water blocking. Moreover, this nature and thickness of the filter cake deposited on the borehole wall will influence the potential for differential pressure sticking to occur [4].
The filtration control additives for water-based drilling fluids can be used to prevent leak-off of water from the drilling fluid to the formation. Organic polymers constitute by far the huge number of filtration-control additives [5].
The control of drilling-fluid filtration is seen as a part of the best drilling practice. Inadequate control of the drilling-fluid property is related to borehole instability, excessive torque and drag, pressure differential sticking, and formation damage. The control of drillingfluid filtration characteristics does not include only control of the filtrate volume per unit area and unit time but also the quality of the resulting filter cake formed in the wellbore [6].
The selection of the efficient drilling fluids is based, basically, on the features of the filter cake formed near wellbore region. Minimizing filtrate loss into the formation by forming a thin filter cake with low porosity and permeability is very critical in order to manage the formation damage problems [7].
Several previous researchers [8-12] highlighted the microscopic structure and chemical composition of the filter cake.
The objectives of this work are to: (1) Measure the main properties of the drilling fluid such as density and rheological at different concentration composition. (2) Study the characterization of filter cake such as thickness, porosity and permeability. (3) Describe the mineralogy and the chemical composition of the filter cake. (4) Compare the laboratory results with the different concentration composition of the drilling fluid.
Experimental Studies
Materials
Water- based drilling fluid was selected for testing in this work. Barite was used as weighting material and bentonite as viscosifier. The features of the ceramic disks which were used have 10 μm mean pore size distribution and permeability of 775 md to stimulate the formation for filtration process at an appropriate temperature and pressure. The porosity of ceramic disk was determined by using the saturated method (the difference in weight of the disk in dried and saturated conditions). The weight of dry condition of ceramic disk was 38.4 g and the weight of wet condition of ceramic disk was 45.9 g. The porosity of ceramic disk can be calculated using Equation 1. It was 37 vol%.
                                                               (1)
          (2)
                                                                   (3)
Where
ф= absolute porosity, volume fraction
Vb= the bulk rock volume, cm3
Vp= pore volume, cm3
D =core sample diameter (6.35 cm)
L =core sample length (0.635 cm)
ρf= 1.0 g/cm3
Preparation of the drilling fluids
The compositions of the drilling fluid samples were prepared in a standard 350 ml laboratory barrel. In other words, each 1 g of material is added to 350 ml of fluid and this is equivalent to add 1 pound of material to 1 barrel of fluid. The compositions of the drilling fluids were used in this study contain the followings: distilled water as the base fluid, Bentonite as viscosifier and filtration control material, Barite as weighting material, Caustic Soda as ph control material, Soda Ash as hardness control material, starch as filtration control material and different concentrations of xanthan gum as rheology control material (0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 g) to select the optimum concentration of XC-Polymer. The compositions of the drilling fluids are given in Table 1. Bentonite is usually added in quantities of (10.5 - 31.5 ppg). According to the desired rheological properties of the drilling fluid, we selected 24.5 g/ 350 ml. Barite is universally used as weighting agent. The quantities of barite needed as weighting agent are given in the formula below:
                                         (4)
Where
W1 = initial weght (ppg)
W1 = desired final weight (ppg)
The amount of barite (52 g) to keep the mud weight as 9.5 ppg. Typical treatment of Soda Ash range from (0.25 to 2 ppg) depended on the calcium level and water chemistry of the drilling fluid, whereas the Typical concentration of Caustic Soda range from (0.20 to 4 ppg) with treatments depended on the calcium level and water chemistry of the drilling fluid.
Properties of the drilling fluids
Drilling fluid density: The mud weight or density was conducted by using a mud balance device. The mud weight of each sample was kept as 9.5 lb/gal (ppg).
Drilling fluid rheological properties: The rheological parameters such as shear stress, shear rate, plastic viscosity, yield point, gel strength of all of the drilling fluids were measured and the apparent viscosity was calculated by using Viscometer Model 900. Table 2 summarizes the properties of the drilling fluids used and (Figures 1-7) show the relationship between shear stress, shear rate and effective viscosity of non-Newtonian fluids at different concentration of XC-Polymer(0.0 g, 0.5 g, 1.0, 1.5 g, 2.0 g, 2.5 g and 3.0 g). The following calculations are performed:
Plastic Viscosity (μp), cp =ф600-ф300                                      (5)
                         (6)
         (7)
                    (8)
Shear rate (γ), sec-1 =1.7023 × ω                                           (9)
Shear Stress (τ), Ib/100ft2 = 1.065 × ф                                  (10)
Where
ф = the dial reading, lb/100ft2
ω = the rotor speed, rpm
It was observed that shear stress increases as the XC-Polymer concentration increases, its maximum value at 3 g/350 ml. On the other hand, the bubbling and flocculation of the fluid with this concentration does not allow using this higher value. However, if more than 2 g of XC-Polymer is added, the fluid loses its property and becomes almost immobile. Experimentally, it was observed that 1g XC-Polymer per 350 ml of the drilling fluid is sufficient for appropriate optimum rheological efficiency. Gel strength is very important property of the drilling fluids as it measures the ability of the drilling fluid to hold solids in suspension. The results showed that there is an increase in the rheology properties of drilling fluid as XC-Polymer increased.
Static HPHT filtration test
To evaluate the filtration properties of the drilling fluid at high pressure and temperature, a standard High Pressure-High Temperature (HPHT) filter press devicewas usedin this work. The fluid put in the HPHT cell and placed in the heating jacket at desirable temperature (212 ºF). The applied pressure was 200 psi as differential pressure. The volume of filtrate was measured in a 30minute period. The density of filtrate was measured by using high temperature density meter (DMA 4500), at different temperature as shown in (Figures 8-14).The filtrate viscosity was measured by using a Brookfield viscometer, at different temperatures as shown in Figure 15.
Results and Discussion
Filter cake thickness
The thickness of filter cake formed on the ceramic disk was measured after completing the HPHT filtration test (T = 212 ºF & P = 200 psi). The tabular results of the thickness of filter cake of the drilling fluid can be seen in Table 3. The results show that there are differences in the thickness of the filter cake of the drilling fluid due to differences in the concentration of XC-Polymer. The thickness was measured where it ranged from 0.102 to 0.186 in. It was observed that there is a decrease in the thickness of the filter cake of the drilling fluid as XC-Polymer increased as shows in Figure 16. The drilling fluid, which has 3.0 g concentration of XC-Polymer, has a small value of thickness. However, at this concentration the mud drilling loses its property and becomes almost immobile and very thick. Figure 17 shows the thickness of the filter cake of drilling fluid sample was obtained from filtration loss test. The filter cake was measured by using Laser and Dial Gauge devices [13].
Scanning Electron Microscopy (SEM) analysis
Scanning Electron Microscopy (SEM) was used to study the structure and the morphology of the filter cake. This technique was used in this work to examine static filter cake formed for water-based drilling fluid. The SEM allows the examination of the filter cake structure and it investigates the effect of the different mud additives in the filter cake [14]. Plank et al. [5] used SEM to study filter cakes containing fluidloss polymers. The Filter cakes were photographed first to obtain a general overview of the broken surface, which provides information on the cake texture. The Scanning Electron Microscope (SEM) analyses of filter cake of the drilling fluid and the average quantitative chemical compositions of the filter cake were showed in Figures 18-25. Scanning Electron Microscopy (SEM) provides high-resolution and long-depthof- field images of the sample surface and near-surface.SEM is one of the most widely used analytical tools due to the extremely detailed images it can quickly provide.
Based on the SEM analysis of the filter cake created with waterbased drilling fluid, it indicates that filter cake contain five main elements. These elements are Sodium (Na), Aluminum (Al), Silicon (Si), Molybdenum (Mo) and Barium (Ba). The results showed that the percentage of Ba in the filter cake is (11-28 %), because the weighting material of the drilling fluid is Barite (BaSO₄) which has a high percentage component in the drilling fluid. Further, it illustrate the distribution of these elements in conjunction with oxygen to form the main phase of the filter cake
Porosity determination
Filter cake porosity: The porosity of the filter cake of the drilling fluid was measured. Table 4 summarizes the porosity of the filter cake of the drilling fluid with different concentrations of xanthan gum (0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 g). Chenevert et al. [15] presented a method that was used to measure the filter cake porosity. The results show that the porosity of the filler cake of the mud drilling ranged to be from 0.866 – 0.813. It was observed that there is a slight decrease in porosity of the filter cake as XC-Polymer concentration increase.
Procedure for filter cake porosity determination: To determine the filter cake porosity the following procedures were applied:
1. By using highly sensitive balance of 0.01 g resolution balance, the dry and wet weight of the ceramic disk was measured.
2. After completing the test of the fluid loss, the filter cake is directly removed from the cell.
3. The wet weight of the ceramic disk and filter cake combination (as 100 % saturated with filtrate) was measured.
4. The weight of wet ceramic disk was subtracted to get the net wet weight of the filter cake.
5. The cake is dried at 200 °F (93 °C) for 24 hour to drive off all water.
6. The dry weight of the ceramic disk and filter cake combination was measured.
7. The weight of dry filter cake was subtracted to get a net dry weight of the filter cake.
Denoting the fluid and grain densities by ρf and ρg respectively, the porosity of the cake фc can be calculated as:
                                                                                      (11)
Where
    (12)
                            (13)
Then rearranging the above equations to get the filter cake porosity as:
                                                                                      (14)
Where
Filter disk porosity: At end of the filtration test (T = 212 ºF & P = 200 psi), the final porosity of ceramic disk was measured by the difference in weight of disk in dried and saturated condition. Table 5 summarizes the calculation of final porosity of the ceramic disk. The results show the change in porosity of ceramic disk. It was measured and ranged from 32 to 34 %. The fluid drilling @ 1.0 g XC-Polymer concentration) has higher porosity than other fluids drilling.
Permeability determination
Filter cake permeability: The permeability of filter cake was measured by using Li et al. [16] method based on Darcy’s Law for liquid flow through an already formed cake and a filter media resistance was included. This method depends on the relationship between the cumulative filtrate volume and time where the slope is equal to flow rate as shown in Figure 26. The flow rate can be obtained from the slope of the straight line region of the filtrate volume vs. time curve, divided by total filtration area. (q/A = filtrate rate, m3/m2.s)
To determine the filter cake permeability the following techniques were applied:
1. Media resistance Km can be determined by a separate clean water flow through filter media only test.
2. Cake thickness Lc and media thickness Lm can be measured.
3. With known Km, Lm and q, pressure drop across filter media Δpm can be calculated based on equation (16).
4. From equation (17) we can be obtained pressure drop across cake Δpc with known total pressure Δpt and pressure drop across filter media Δpm.
5. Finally, with known q, Δpc, μ and Lc, permeability of cake can be then determined from equation (18).
Figure 26: Li et al. [16] atypical volume of filtrate against time curve
Where
Rt = Total resistance
Rm= Resistance of cake
Rc = Resistance of filter media
q = filtrate rate, m3/m2-s
Km = filter medium permeability, m2
Kc= filter cake permeability, m2
Lm = thickness of filter medium, m
Lc = thickness of filter cake, m
μ = filtrated fluid viscosity, Pa.s
Δpm = pressure drop across the filter medium, Pa
Δpc= pressure drop across the filter cake, Pa
Δpt= total pressure drop, Pa
Figures 27-32 show the relationship between the cumulative filtrate volume and time.
Table 6 shows the average permeability of the filter cake. The permeability of the filter cake was calculated. It ranged from 0.258 to 0.571μd. The results show that the permeability of filter cake decrease as XC-Polymer increase. It was observed that the average permeability of the filter cake was decreased as the concentration of XC-Polymer increased
Filter disk permeability and reduction in permeability: The change in permeability of the ceramic disk can be obtained from Equation 19, which developed by [17,18]
Where
Kinitial= initial permeability of ceramic disk, md
Kfinal = permeability of ceramic disk after filtration process, md
фi = initial porosity of ceramic disk, volume fraction
фf = final porosity of ceramic disk after filtration process, volume fraction
Therefore, the damage ratio was determined by taking the ratio of the final permeability of the ceramic disk (kf) to the initial permeability of the ceramic disk (ki). Mathematically, the damage ratio, in percentage, is shown in the following equation:
Table 7 summarizes the calculation of final permeability of ceramic disk and the reduction in permeability. The results show that the concentration of XC-Polymer was changed from 0.0 to 3.0 g as shown in Figure 33. This plotted was constructed to obtain the optimum concentration of XC-Polymer for less damage. The reduction in permeability was 35% at 0.0 g of XC-Polymer concentration. It decreased to 29% from 0.0 to 0.5 g, also decreased to 22.5% from 0.5 to 1.0 g, and then increased to 31.35% from 1.0 to 1.5gm. The analysis of the results shows that at above 2.0 lb/bbl concentration of the XCPolymer, the effect of XC-Polymer on formation damage is stabilized at constant value. Thus, the concentration of XC-Polymer, which has a less reduction in permeability, is 1.0 g.
Conclusions
In this study, we prepared and examined seven samples of waterbased drilling fluid, which contained the same composition with different concentrations of XC-Polymer additives to select the optimum concentration of XC-Polymer and evaluate the filter cake characteristics. Based on the results obtained, the following conclusions may be drawn:
1. There is an increase in the rheology properties of drilling fluid as XC-Polymer increased.
2. SEM analysis provided a good method to study the structure and morphology of the filter cake. Further, it allowed knowing the average quantitative chemical compositions of the filter cake.
3. The thickness of the filter cake of the drilling fluid is decrease as XC-Polymer increased.
4. There is a slight decrease in porosity and permeability of the filter cake as XC-Polymer concentration increase.
The analysis of the results shows that at above 2.0 lb/bbl concentration of the XC-Polymer, the effect of XC-Polymer on formation damage is stabilized at constant value. Therefore, the concentration of XCPolymer, which has a less reduction in permeability, is 1.0 g.
References

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