幻灯片 1

幻灯片 1

Studies on the Impacts from Different Activators and Inorganic Components of Curing Agents on Performance of Solidifiable Plugging Fluid Author: Xiaoyang Guo,Zhizhong Deng,Zaoyuan Li Public Speaker Zhizhong Deng Units name:Southwest Petroleum University Contents Reach Background Experiment Measured Conclusion Reach Background The issues are raised in the context of how come ? To solve the problems occurring during the treatment process in the case of any malignant lost circulation, we studied a type of new solidifiable gel plugging fluid system. What are the aspects of mutual concern still need improving to handle the lost circulation? The door sealed phenomenon is caused during the addition of the blocking materials to the drilling fluid, when the weak gel fails to significantly improve the stratum bearing capacity, causing the gel plugging agent to be easily eroded; this erosion results in a lack of strength in the later period. a. Permeable loss c.induced fractures loss b. Natural fractures loss d.Cavern loss Fig. 1 the various types of Lost Circulation Relevant theories The theories are now the tail sealing theory, stress cage and fracture closure stress theory, all of which require the formation of an effective packing zone supported by a

certain strength. The engineering demands set specific requirements on the material properties Leakage Channel Plugging Agent Wellbore Bore Weak Gel or Cement Focus Formation Most of the reports focus on the impact of the additives on the cementing material; in contrast, the impact of the percentage change of cementing material components on the rheology and strength is rarely reported. b. Erosion a. Door Sealed Solidifiable Plugging Fluid C. Form a Packing Zone Fig. 2 Sketch of the Plugging Effect Materials Primary components of the solidifier: CaO, SiO2, Al2O3 and MgO, with an average particle size at the surface of 5.806 m.m. Table 1 Main Solidifier Components and Contents SiO2 Al2O3 Fe2O3 27.15% 19.16% 2.12% CaO 31.37%

MgO 8.64% Surface Area (m)%) Particle Size (m)m.m) Fig.3 Distribution of the Particle Size of the Solidifier Other 11.56% Hydration Mechanism of the Solidifier The determinant of the solidifier hydration rate is the activity of the reactionless vitreum on the particle surface. The vitreum in the solidifier is a kind of microheterogeneous substance and its basic structural unit are the [SiO4]4- and [AlO4]5- tetrahedron composed by network particles, while the Ca2+, Mg2+ and the six-coordinated Al3+ etc. particles that may alter the network will be outside the network chain, however, these particles will also be distributed in the network structure in the form with certain coordination . In order to activate the activity of the solidifier, the solidifier must be in the solutions of polar molecules or OH- ions; these polar molecules or OH- ions can break down the ionic bond and covalent bond and the solidifier will break up into [SiO4]4- and [AlO4]5- as well as Ca2+, Ca(m)OH)+ etc. cations; within the solution supersaturated with hydration products dispersed and decomposed from the solidifier particles, the hydration products continuously nucleated and developed, and final products will overlapped between each other to form the jelling network structure. Impact of the Bentonite on the Base Mud Bentonite is the major component of drilling fluid. The main purpose of adding bentonite to base mud is to adjust the sedimentation stability, shear thinning behavior, and compatibility to prepare the mud for a stable performance. Mg6Fe2CO3(OH)164H2O MgAl(OH)14.xH2O Ca3Al2(OH)12 Mg2Al(OH)7 Ca3Al2O6 SiO2 CaCO3 Na2Si2O5 Adding the bentonite

0 10 20 30 40 50 60 Without adding the bentonite 2/( ) Fig. 4 XRD Analysis after Adding Bentonite Bentonite is an important component of the drilling fluid. While meeting the performance of the plugging fluid, bentonite is sufficiently compatible with the drilling fluid. This compatibility indicates that the performance change of the plugging fluid is not caused by the difference of the components of the solidification products of the plugging fluid, but by the change of the microstructure of the solidified material. CaO SiO2 MgO Al2O3 Fe2O3+NaOH+Na2CO3+Na2SiO3 CaCO3+Mg6Fe2CO3(m)OH)16.4H2O+Mg2Al(m)OH)7+ Ca3Al2O6+ SiO2+Na2Si2O5+MgAl(m)OH)14.xH2O+Ca3Al2(m)OH)12 The SEM microscopic analysis of the test samples with bentonite a. Base Mud without Bentonite b. Base Mud with Bentonite

Fig5 SEM analysis The SEM microscopic analysis of the test samples with bentonite indicates that the microstructure of the plugging fluid solidification product without the addition of bentonite (m)Fig. 5a) is looser and that there are fewer filling materials between the different structures. As a solid phase particle, bentonite is effectively distributed among the different particles (m)Fig. 5b) to realize close packing, which helps the strength intensification and shear force increase after the solidification of the plugging fluid. Impact of the Bentonite on the Base Mud Rheology 80 70 70 60 1% 50 2% 40 3% 30 4% 20 5% Viscosity mPa.s Shear Force Pa 0% 1%

2% 3% 4% 5% 0% 60 50 40 30 10 0 0 20 100 200 400 600 800 1000 1200 200 300 400 500 600 700

800 900 1000 1100 Shear Rate S-1 Shear Rate s-1 Fig. 6 Shearing Force at Different Shear Rate in general, the viscosity increases with the increase of the amount of bentonite, and there is almost no viscosity difference for both no added bentonite and the addition of 1%. Fig. 7 Effective viscosity A fraction of the water molecules are adsorbed onto the surface of lattices to reduce the free water. The end-end structure becomes the end-face structure, which effectively forms the spatial network in the base mud, thus causing the increase of viscosity. Impact of Bentonite on the Suspension Stability Bentonite can improve the viscosity of the base fluid and realize a stable suspension of the solidifier in the base mud. According to the Stoke Law: 0% 1% 2% 3% 4% 5% Pressure Gradient Pa/mm

100 80 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 Velocity mm/s Fig. 8 Pressure Gradient for Different Velocities Given that the solidifier particle size is taken as 5.806 m according to the laser particle size analyzer, the density difference is 1.65 g/cm3 and the viscosity is 30 mPa.s, the settling velocity is calculated as 110 -3 cm/s according to the Stoke Law, and the time is 990 s for settling or subsiding for 1 cm to occur. Impact of CaO on the Compressive Strength of the Plugging Fluid NaSi2O3(OH)3H2O Ca3AlFe(SiO4)(OH)8 MgAl(OH)14xH2O

Na22Si4O9 Adding the CaO Without adding the CaO 0 10 20 30 40 50 60 50 C*24h 9 Strength Mpa CaSi 10 Ca(OH)2 Ca5(SiO4)2CO3 50 C*48h 8 90 C*24h 7 90 C*48h

6 5 4 2/( ) 3 32 Fig. 9 XRD Analysis after the Addition of CaO 34 36 38 40 CaO content % 42 44 Fig. 10 Compressive Strength for Different CaO Percentages The compressive strength of the plugging fluid is the highest when the CaO percentage in the solidifier reaches 33%. After the dissolution of CaO, a saturated Ca(m)OH)2 solution is rapidly generated on the surface of the solidifier vitreum, which promotes the early strength agent to destroy the vitreum on the solidifier surface to cause the hydration reaction of the activated calcium-rich phase and silicon-rich phase of the solidifiers and to ensure a shorter setting time for the plugging fluid and higher early strength. 46 a. 33% of CaO Percentage in the Solidifier b. Over 33% of CaO Percentage in the Solidifier Fig.11 SEM analysis

Various structures are connected by the coarser fabric tissues, and the gaps among the structures are well filled. As a result, the compressive strength of the plugging fluid solidification is higher when the CaO percentage is 33% in the solidifier. The microstructure of the solidified plugging fluid is looser when the CaO percentage is over 33% in the solidifier (m)Fig. 11b), and the structures are cross-linked by fine fibrous materials, so its compressive strength is lower. Impact of the MgO Content on the Solidifier Performance 13 12 50 C*24h Mg2Al(OH)7 11 50 C*48h Adding the MgO Strength MPa Mg6Al2(OH)184.5H2O Mg(OH)2 10 9 8 90 C*24h 90 C*48h 7 6

5 Without adding the MgO 0 10 20 30 40 50 60 2( ) Fig. 12 XRD Analysis after the Addition of MgO 4 10 12 14 16 18 20 22 MgO Percentage % Fig. 13 Compressive Strength for Different Percentages of MgO The studies indicated that, when MgO is maintained at 50, there is no strength until the MgO percentage reached 18% and that the strength is higher

than 8.5 MPa. The strength increased with the increase of MgO percentage. When MgO is maintained at 90, the strength increased with the increase of the MgO percentage. The maintenance period is prolonged for 24 h, and the strength increases, on average, by 0.85 MPa. 24 26 14 50 C*24h 50 C*48h Strength MPa 12 90 C*24h 10 90 C*48h 8 6 4 8 9 10 11 12 13 14 15

16 17 18 MgO Percentage % Fig. 14 Compressive Strength for Different Percentages of MgO (m)with added CaO) The results indicate that the overall trend of the strength first increases and then decreases with the increase of the MgO percentage (m)Fig. 14). The plugging fluid strength is the highest when the MgO percentage is in the range of 12 to 16%. Fig. 15 SEM Analysis Sketch for the Addition of MgO The microstructure of the solidified plugging fluid is very compact when the percentage of MgO in the active solidifier is 16%, with the gaps among the structures being well filled, and the structures are cross-linked Fig. 15 . Therefore, the solidified plugging fluid presents a higher compressive strength. Impact of the Al2O3 Percentage on the Solidifier Performance 8 10 90 C*48h 9 6

Strength MPa Strength MPa 7 90 C*24h 5 4 3 50 C*24h 50 C*48h 8 90 C*24h 7 90 C*24h 6 5 4 2 20 25 30 35 40 45 AL2O3 Percentage % Fig. 16 Compressive Strength for

Different Percentages of Al2O3 There is no strength in the plugging fluid after maintaining Al2O3 for 48 h at 50 (m)Fig. 16), and its strength reaches the maximum value when the percentage of Al2O3 is 27% at 90; the strength decreases for percentages of Al2O3 greater than 27%. 3 18 20 22 24 26 28 30 32 AL2O3 Percentage % Fig. 17 Compressive Strength for Different Percentages of Al2O3 (m)with added CaO) The results indicated that the strength of the plugging fluid is the highest for no added Al2O3 (m)Fig. 17). The compressive strength decreased with the increase of the amount of added Al2O3, and the strength degradation is more obvious with the amount of added Al2O3 less than 27%. Impact of the SiO2 Percentage on the Solidifier Performance 8

50 C*24h 7.5 50 C*48h Strength MPa 7 6.5 90 C*24h 6 90 C*48h 5.5 5 4.5 4 3.5 29 30 31 32 33 34 35 36 37 38 39

SiO2 Percentage % Fig. 18 Compressive Strength for Different Percentages of SiO2 (m)with added CaO) SiO2 is an inert substance. SiO2 can realize the effective filling in the components and plays an important role in the strength degradation of the test samples in the later stage. The studies indicate (m)Fig. 18) that there is no obvious strength change when the amount of added SiO2 is less than 31%; with a further increase above 31%, the strength decreases significantly. Conclusion no new substance is generated after the addition of bentonite. The bentonite forms the spatial network structure through hydration, which can effectively change the rheology and sedimentation stability of the plugging fluid. In the single component test of MgO, the compressive strength is at a maximum when its percentage reaches 26%; in the tests when CaO is added in respective mixtures with MgO, Al2O3 and SiO2 , the compressive strengths are all greater than 3 MPa. During field construction, the actual working conditions can be used to adjust the flow profile index, viscosity coefficient and solidification strength to meet the requirements of the plugging construction. Thank you!

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