Lab 3—Effect of Bentonite and Barite on Filtration Properties
Drilling and Production Engineering Lab
PE 4331-008 Group D
February 26, 2016

Eric Ohman
David Farrier
Lucas Fischer
David Hernandez

Academic Integrity Statement
On my honor, I affirm that I have neither given nor received inappropriate aid in the completion of this exercise.
Name: Eric Ohman _ Date: 02/26/2016
Name: David Farrier _______Date: 02/26/2016
Name: Lucas Fischer ______ Date: 02/26/2016
Name: David Hernandez Date: 02/26/2016
ABSTRACT
Several experiments were conducted on various drilling fluid samples, chiefly relating to the effects of viscosifiers (Bentonite), weighting agents (Barite, and salt on the filtration properties of these muds. Clear knowledge of the filtration properties of drilling fluids is of great importance to the drilling engineer as excessive filtration can cause both damage to the formation both from fine particles and from water infiltration. There are many negative effects of excessive filtration, including the loss of expensive drilling fluid, damage to the formation, and stuck pipe caused by large amounts of filter cake. In this experiment, using mud cakes were formed from mud samples of varying composition using a filter press. These results were then analyzed in fluid loss vs. square root of time curves in order to determine spurt and API filtration loss. The thicknesses of the filter cakes were also determined. It was determined that spurt loss tended to increases with both bentonite and barite concentration. API filtrate loss tended to increase with Bentonite concentration and decrease with Barite concentration. Filter cake thickness also tended to show a direct relationship between solids concentration. The cake thicknesses ranged from 2.60 - 3.21 mm and the API filtrate losses ranged from about 14-22 mL.

INTRODUCTION
Drilling fluid system design is one of the most important tasks in any drilling operation. Drilling mud is a complex mixture of various additives. These additives are added in varying amounts throughout the drilling process of a well in order to control the rheological properties of the drilling fluid. These rheological properties of the mud determine how the drilling mud will perform in various formations and operating conditions. One important parameter to monitor throughout drilling operations is the filtration loss induced by a drilling mud.
In short, filtration loss is the process in which drilling mud filtrate enters a permeable formation. This process typically occurs in phases. First, “spurt” invasion occurs when the drill string exposes the fresh rock of the formation and the immediate surrounding mud proceeds to contact the walls and seep into the formation. As this occurs, the solids in the drilling mud begin to block pores and form a thin layer of mud, known as a mudcake. As this process continues, the mudcake serves as a filter and impedes further invasion of the whole mud into the formation and the only component to penetrate the mudcake and flow into the formation is known as filtrate (Zhan 2009). Thus, this is now considered filtrate invasion.
Excessive filtrate loss can create significant problems for the operator, not only in the drilling phase, but also the producing phase of the well’s life. If filtrate invasion continues at an undesirable rate, it will displace the formation fluids and cause formation damage. This damage to the formation will inhibit potential production rates and ultimately reduce the effective EUR of the well. Mitigation efforts by the operator would introduce unanticipated stimulation costs (Claas 2006). Rather than mitigating these issues, the best solution is prevention; this can be achieved by simulation of your reservoir to assess formation damage and well-productivity. The simulation models the filter cake buildup under both static and dynamic conditions, the transport of solids, and the fluid loss to formation amongst other parameters to asses the implications caused to the well further in its producing life (Lohne & Han 2010)
A high quality and effective drilling fluid program is one of the primary components necessary to optimize drilling operations. By closely monitoring drilling mud properties such as filtrate loss and invasion throughout the drilling process, an operator can reduce the overall drilling cost of a well and ensure optimal conditions for a long and fruitful producing life further down the road.

OBJECTIVES 1. To study filtration properties of drilling fluids. 2. To examine the effects of: viscosifier bentonite, weighting agent barite, and salt on filtration properties of drilling muds.

THEROY Filtration rate can be found using Darcy’s law. For filtration loss, Darcy’s Law is used to calculate the flow of mud filtrate through a mudcake. The rate of filtration is given in equation 1. dVfdt=kA∆Pμhmc ………………………………………………………………………………………………………………………………………... (1) In calculating spurt loss of a fluid, trace a tangent line from the later filtrate volumes to the y-intercept. With the spurt loss and filtrate volume at 7.5 minutes, the API filtration loss can be estimated at 30 minutes with equation 2. V30=2V7.5=Vsp ……………………………………………………………………………………………………………………………….. (2) This equation was derived from equation 3, which was developed from Darcy’s Law. Vf= 2k∆Pfscfsm-1Atμ ……………………………………………………………………………………………………………… (3) These equations operate under the assumptions of laminar flow with a single, incompressible fluid.

EXPERIMENTAL STUDY i. Materials: a. Fresh Water b. Bentonite Clay Viscosifier c. Barite Weighting Agent d. Salt ii. Equipment: a. Mixing Blender (Fig. 1) b. Filter Paper (Fig. 2) c. API Filter Press (Figs. 3 and 4) d. Electronic Scale e. 500 ml Graduated Cylinder f. Thermometer g. Small Graduated Cylinder iii. Procedure:
Six samples were prepared using the mixing blender. Samples A through F contained 500 mL of fresh water and the following compositions; (A) 42.9 g bentonite, (B) 46.5 g bentonite, (C) 50.0 g bentonite, (D) 42.9 g bentonite and 50.0 g barite, (E) 42.9 g bentonite and 100.0 g barite, and (F) 42.9 g bentonite and 10.0 g salt. Figs. 1 and 2—Mixing Blender and Filter Paper
The filter cell and o-ring was cleaned and dried, and then the first sample was loaded into the cell, filling the cell up to about a quarter of an inch from the placement of the o-ring. The o-ring is placed and then the filter paper above that. The filter cell is inserted into the pressure manifold, which should be set to 100 psi. Pressure is gradually applied to the cell until the first drop of filtrate comes out and is collected in a graduated cylinder. Filtrate volume is then measured at 30 seconds and 1, 2, 3, 4, 5, 7.5, and 10 minutes. After 10 minutes the cell is depressurized and the filter cake thickness is measured. Figs 3 and 4—Pressure Manifold, Filter Cell, and O-Ring iv. Raw Data:
TABLE 1—SAMPLE FILTRATE VOLUMES IN CC AND TEMPERATURES

TABLE 2—CAKE THICKNESSES

DATA ANALYSIS AND INTERPRETATION

Sample | | A | B | C | D | E | F | Spurt Loss (Vsp) (1) | ml | -0.459 | 0.151 | 0.280 | -0.036 | -0.401 | .404 | Spurt Loss (Vsp) (2) | ml | -0.963 | 0.003 | 0.392 | -0.234 | 0.076 | -0.167 | API Filtrate Loss (V30) | ml | 14.86 | 15.05 | 14.52 | 15.24 | 13.20 | 22.00 | Mass of Bentonite | g | 42.90 | 46.50 | 50.00 | 42.90 | 42.90 | 42.90 | Mass of Barite | g | 0 | 0 | 0 | 50.00 | 100.00 | 0 | Mass of Salt | g | 0 | 0 | 0 | 0 | 0 | 10.00 | Volume of Water | ml | 500.00 | 500.00 | 500.00 | 500.00 | 500.00 | 500.00 | Total Mass | g | 541.95 | 545.55 | 549.05 | 591.95 | 641.95 | 551.95 | Weight % of Bentonite | | 7.92 | 8.52 | 9.11 | 7.25 | 6.68 | 7.77 | Weight % of Barite | | 0 | 0 | 0 | 8.45 | 15.58 | 0 |

Table 2 – Spurt loss, API Filtrate loss, and weight percentages of samples A-F When observing Table 2, spurt loss trended to increase with the increase in bentonite concentrations in mixtures A, B, and C and similarly with the increase in barite in samples D and E. Spurt loss was calculated twice, in order to find the best trend. Spurt loss (1) is calculated using Equation 2 below. …………………………………………………………………………………………………………... (2) Spurt loss (2) is calculated from plotting the filtrate volumes, deriving a best fit linear trend equation, and then solving for the intercept. These equations are shown in Figures 1, 5, and 9. Spurt loss (2) is used for further calculations as the data is directly derived as the y intercept on each trend line equation.

Sample | | A | B | C | D | E | F | Volume of Bentonite | ml | 16.19 | 17.55 | 18.87 | 16.19 | 16.19 | 16.19 | Volume of Barite | ml | 0 | 0 | 0 | 11.82 | 23.64 | 0 | Volume of Salt | ml | 0 | 0 | 0 | 0 | 0 | 4.61 | Volume of Water | ml | 500 | 500 | 500 | 500 | 500 | 500 | Total Volume | ml | 516.19 | 517.55 | 518.87 | 528.01 | 539.83 | 520.80 | Volume % of Bentonite | | 3.14% | 3.39% | 3.64% | 3.07% | 3.00% | 3.11% | Volume % of Barite | | 0.00% | 0.00% | 0.00% | 2.24% | 4.38% | 0.00% |

Table 3 – Volume percentages of barite and bentonite for samples A-F Table 3 demonstrates the volume percentage of barite and bentonite, which can further be used in the filtration equation below to find volume of filtration in Equation 3 below. ……………………………………………………………………………………………. (3) Mass concentration is used in the following figures, but has a linear relationship to volume concentration through material density. Therefore, the figures expressing spurt loss and API filtrate loss as a function of mass concentration coincide with those of volume concentration.

Fig. 1 – Filtrate Volume as a function of the square root of time for samples A-C

Fig. 2 – API Filtrate Loss per concentration of bentonite by weight for samples A-C

Fig. 3 – Spurt loss per concentration of bentonite by weight for samples A-C

Fig. 4 – Filter cake thickness per concentration of bentonite by weight for samples A-C

Figure 1 demonstrates the increase in filtrate volume over time and the equations from each trend line are be used to calculate the volume of filtrate at 30 minutes as well as spurt loss for samples A, B, and, C. The R^2 values given for each equation are above 95% which means our samples were well recorded and our data fits a strong linear trend, with only a few anomalies noticed in sample A. From Figures 3 and 4, the filter cake thickness and spurt loss tended to increase with concentration of bentonite. The only inverse relationship observed was between API filtrate loss and bentonite concentration in Figure 2.

Fig. 5 – Filtrate Volume as a function of the square root of time for samples A, D, and E

Fig. 6 – API Filtrate Loss per concentration of bentonite by weight for samples A, D, and E

Fig. 7 – Spurt loss per concentration of bentonite by weight for samples A, D, and E

Fig. 8 – Filter cake thickness per concentration of bentonite by weight for samples A, D, and E

Figure 5 demonstrates the increase in filtrate volume over time and the equations from each trend line are be used to calculate the volume of filtrate at 30 minutes as well as spurt loss for samples A, D, and, E The R^2 values given for each equation are above 99% for samples D and E, concluding that the spurt losses and API filtration losses are accurate. Figure 6 demonstrates an inverse correlation between API filtrate loss and barite concentration, dissimilar to samples mixed with bentonite (A, B, and C). Figure 7 relates to Figure 4 as increasing amounts of barite and bentonite tend to increase spurt loss. The filtrate thicknesses observed in Figure 8 are equal for samples D and E suggesting that increasing the barite concentration will only leave a marginal impact on filtrate thickness. Both samples D and E showed considerably less (.5 mm) cake thicknesses than sample A.

Figure 9 - Filtrate Volume as a function of the square root of time for samples A and F

Sample | Spurt Loss (Vsp) (1) | Spurt Loss (Vsp) (2) | API Filtrate Loss | Filter Cake Thickness | Mass of Salt | Mass of Bentonite | | ml | ml | ml | mm | g | g | A | -.459 | -0.963 | 14.86 | 3.06 | 0 | 42.9 | F | .404 | -0.167 | 14.86 | 2.60 | 10.00 | 42.9 |

Table 4 – Samples A and F spurt loss, API filtrate, and cake thicknesses

Mixture F recorded some of the lowest filtrate losses of this experiment and the highest filtrate volumes over 10 minutes of recording. The addition of 10 grams of salt went a long way to reduce filtrate cake thickness and increase filtrate volume, and produce the steepest slope with 99.9% linearity observed in plots similar to Figure 9. From Table 4 and Table 2, sample F recorded average API filtrate losses and the highest recorded spurt loss, according to Equation 2. The cake thickness of sample F was considerably low on average compared to the rest of the samples. Samples D and E deomonstrated lower cake thicknesses due to the inclusion of barite instead of bentonite, but the addition of 10 grams of salt lowered sample F thickness below samples A-C.

CONCLUSION
It was shown in these experiments that spurt loss tended to increase with both bentonite and barite concentration. The API filtrate loss tended to increase with Bentonite concentration and decrease with Barite concentration. Filter cake thickness was shown to be directly related with the concentrations of both Bentonite and Barite. Filter cake thickness ranged from 2.60-3.21mm and the API filtrate losses ranged from about 14-22 mL

REFRENCES

Zhan, W. 2009. Dynamic Filtrate Loss During the Drilling of a Horizontal Well with High-Permeability Contrasts and Its Impacts on Well Performance. SPE Reservoir Evaluation & Engineers 12(6): 886-897. SPE-110677-PA. http://dx.doi.org/10.2118/110677-PA

Lohne, A. and Han, L. 2010. Formaion-Damage and Well Productivity Simulation. SPe Journal 15(03): 751-769. SPE-122231-PA. http://dx.doi.org/10.2118/122241-PA

Claas, Z. 2006. Benchmarking the Formation Damage of Drilling Fluids. SPE Production & Operations 21(1): 40-50. SPE-86544-PA. http://dx.doi.org/10.2118/86544-PA

Bourgoyne, A.T., Millheim, K.K, Chenevert, M.E., Young, F.S. 1986. Applied Drilling Engineering. Textbook Series, SPE, Richardson, Texas 2: 41-55.

APPENDIX A – EQUATIONS dVfdt=kA∆Pμhmc ………………………………………………………………………………………………………………………………………... (1) V30=2V7.5=Vsp ……………………………………………………………………………………………………………………………….. (2) Vf= 2k∆Pfscfsm-1Atμ ……………………………………………………………………………………………………………… (3)

APPENDIX B – TABLES

| Density, g/cc | Bentonite | 2.65 | Barite | 4.23 | Salt | 2.17 | Water | 0.998 |

Table 5 – Densities of materials used to calculate volume concentration of bentonite and barite.

APPENDIX C – FIGURES

Figure 10 – Sample A filter cake

Figure 11 – Sample B filter cake

Figure 12 – Sample C filter cake

Figure 13 – Sample D filter cake

Figure 14 – Sample E filter cake

Figure 15 – Sample F filter cake