An Experimental Study to Assessing the Efficacy of Oil to Prevent Differential Stuck Pipe Incidents in Zubair Oil Field, Southern Iraq

Abstract


Introduction
Zubair oil field is known for its complex geological formations; because of the many diagenesis and deposition processes involved, carbonate sediments and rocks exhibit a variety of physical features (Al-Baldawi, 2020).Awadeesian et al. (2019) have recently shown that the Mishrif Formation is formed up of 32 structures that produce oil and major carbonate reserves.The risk of differential stuck pipe is associated with wells drilled in Zubair field, particularly if the well passes through the Mishrif Formations in the Middle Cretaceous, regarded as the primary producing reservoir (Idan and Salih, 2023).According to Aqrawi et al.)2010), the major oilfields are common in Rumaila, West Qurna, Zubair, Majnoon, and Nahr Umr, which also have the most significant oil accumulations.Oil reservoir brines are extremely common geological fluids that coexist with hydrocarbons.The chemistry of Brine constrains fluid flow and predicting reservoir scales (Awadh et al., 2019).These oilfields are characterized by large north-south trending anticline structures.Permeability is affected by the clay minerals that are released from the shale units in the Zubair Formation (Awadh et al., 2014).Differential-pressure pipe sticking is one of the most prominent issues with drilling and the main reason for excessive non-productive time.It typically happens in porous or depleted formations because the drill string had to be moved to connect a new pipe, take trips, and fix a drilling problem.Due to the pressure differential between the formation and the wellbore and the strong filtration in a high permeability zone, the drill string becomes stuck in the filter cake as it becomes immobile.The drill string cannot move in the wellbore because of the adhesion bonds formed at the pipe/filter-cake interface due to the combined action of adhesive and cohesive forces in the area of the sticking zone.Therefore, it cannot be rotated or reciprocated by the driller without being freed using mechanical or chemical processes (Alshaikh, 2019).
Numerous studies have determined the best ways to avoid and treat the differential stuck pipe to minimize excessive pressure in the borehole when working into depleted reservoirs.The level of depletion should be considered the non-rotating times must be kept as minimal as possible Charlez and Onaisi (1998).Issa and Al-Haleem (2022) primarily concentrated on mechanical pipe sticking in their chosen experiments.The study aimed to identify the stuck pipe issue in the Zubair oil field by selecting four wells.They concluded that mechanical pipe sticking can be avoided by using a greater flow rate and that other parameters, including yield point (YP), plastic viscosity (PV), drill string rotation speed, penetration rate, and cutting density, can affect flow rate values.Amina and Al-Haleem (2018) conducted a study to examine the differential stuck pipe occurrences in Khabaz Oilfield.
Well Khabaz-34 was selected to investigate the problem of stuck pipes in this oilfield.The instances involving stuck pipes were examined using the graphing analytic application Easy View.Ultimately, they recommended modifying the casing seat design and utilizing the proper drilling mud with the appropriate rheology properties to reduce the possibility of a stuck pipe.Al-Mahdawi and Saad (2018) evaluated the efficiency of silicon oxide nanoparticles using the LTLP filter press.They found that the amount of filtrate decreases as the concentration of nanoparticles increases.Al-hisnawy and Al-Haleem (2023) used a new technique utilizing well force from the Mishrif Formation to release a stuck pipe, develop the right drilling mud weight to avoid this problem in the future and assess the time and cost savings compared to the usual method.Fadhil and Al-Haleem (2022) The shale cuttings from the Tanuma and Zubair formations were characterized using a stereomicroscope, and the shale structure was examined using a scanning electron microscope.It was found that the opposite is false and that the drilling mud designed for Tanuma shale can be used to drill Zubair shale.It was also found that the shale rocks are dispersed in fresh water and can be stabilized by adding inorganic additives (KCl).Halliday and Clapper (1989) One method for minimizing differential sticking is to use oil to raise the coefficient of lubricity and lower the propensity of water-based drilling fluid to stick.
For this, petroleum oils, either refined or unrefined, have been used in the past.But, the use of oil is limited by environmental regulations.The authors suggest using various materials, including soaps, detergents, fatty acids, asphalts, and commercial lubricants, as a substitute for diesel oil.However, Alternatives to diesel oil include soaps, detergents, fatty acids, asphalts, and commercial lubricants such as vegetable oil/glycol blends, ester blends, and blends of glycol surfactant.These alternatives seek to offer comparable lubricating qualities in a more eco-friendly manner.
This research aims to determine how bentonite clay affects the characteristics of drilling mud and how using oil may decrease this effect.To choose the optimal mud properties, it can demonstrate an overview of spotting fluids and a review of the testing procedures for adding oil and their impact on rheological characteristics, torque, and friction coefficient.The outcome can be used to create drilling fluid that won't cause differential pipe sticking.

Area of Study
One of the biggest fields in southern Iraq is Zubair oil field, approximately 20 km southwest of Basra, as shown in Fig. 1.This field is known for its complex geological formations, characterized by varying permeability, fault zones, and depleted zones, Zubair field was selected to study the problem of a differential stuck pipe that occurred while tripping out in Mishrif Formation and procedure steps to formulate the appropriate method to release the stuck string.

Stratigraphic Column
Many Iraqi oilfields have a stratigraphic column that ranges from the Upper Jurassic to Tertiary Ages (i.e., stretches from the bottom of Sulaly formation to Dibdiba formation), as illustrated in Fig. 2. It is mostly made up of thick carbonate layers interspersed with clastic rocks.Mishrif Formation (carbonate) and Zubair Formation (clastic) are major reservoirs within the Zubair oilfield that contain vast volumes of hydrocarbons derived mainly from the Cretaceous Period (Jassim and Goff, 2006).

The Material Used
350cc of fresh water, bentonite clay and several chemical additives, such as carboxy methyl cellulose (CMC), partially hydrolyzed polyacrylamide (PAC-LV), and oil lubricants were among the various components used in the study, the specific types and quantities of chemicals used are shown in Table below.

Experimental Setup and Procedure
The coefficient of friction is determined using a lubricity tester in accordance with accepted practices, and the rheological characteristics are determined using a Fann VG viscometer.Figure 3 depicts a self-made experimental setup used to calculate sticking torque.

VG Viscometer Fann
A direct-indicating viscometer, commonly known as a V-G meter, measures drilling mud's viscosity and gel strength.The most accurate indication of viscosity is measured by the revolving cylinder and bob viscometer.There are two rotating speeds on every instrument: 300 and 600 rpm.

The Self-fabricated Description
A self-made equipment setup used to gauge mud's tendency to stick is shown in Figs. 3 and 4. The mud filtering cell, a torque wrench, and a syringe pump are some of the parts of the setup.The syringe pump pressurizes the mud throughout the filter cell to start the process.A spring steel wire has taken the position of an O-ring seal that was formerly situated in the middle of the top-end cap.A new entrance valve is made to enable the hydraulic line from the syringe pump to become pressurize the cell.The polished steel ball that rests on the filter media is connected to the wire made of steel inside the cell.The wire's extremity that emerges from the cell has a torque gauge fastened.To finish the test, replace the topmost cap., insert the paper filter into a cell, fill the cell with mud, and set up the torque gauge and ball.The test holds the mud like a typical fluid-loss measurement to assess the mud's tendency to stay.A differential pressure of 400 psi is used for testing (according to overbalance, which resulted from the mud weight used in the study case, it is considered within the range of actual drilling conditions).As the filtering process continues, the filter cake contains the steel ball.After 30 minutes, the torque gauge spins to determine how much effort is needed to extract the ball.This calculates the required torque.

The Procedure of Experimental
Addressing the challenges of differential pipe sticking during drilling involves a systematic approach.Initially, precise measurements are conducted to determine the friction coefficient and force required to release a stuck ball in a bentonite water suspension.Subsequently, a drilling fluid is formulated, deliberately excluding the ingredient responsible for controlling the sticking tendency.The properties of this modified drilling fluid are estimated, including rheology, filtration loss, friction coefficient, and the torque required to free the stuck ball.Finally, a sticking tendency controlling additive is introduced to the drilling mud, and the same properties are measured again.

The problem
Well-A was drilled to the third and fourth pay formations, with a measured depth of 3738m and a TVD of 3573m, with a maximum inclination of 24.19°.Many problems were encountered while drilling the 12 1/4" hole section, MW=1.18 sg, including complete losses through the Mishrif Formation (2347 to 2400 m) and differential stuck pipe at 2376m.It has a big impact on how effective and costly the well drilling becomes.Pipe sticking happens around 50% of the time during tripping, 10% when bottom drilling, 20% when operating the pipe at a connection and reaming, and 20% during other operations (Kayode, 2020).Reid et al. (2000) have recently shown that the use and operational procedures for applying this novel spotting fluid can be used to monitor and optimize drilling mud properties.This test allows operators to evaluate the drilling mud's efficiency in reducing the likelihood of differential sticking.By monitoring key parameters and properties of the drilling mud, such as rheology, filtration control, and lubricity, operators can make informed decisions to adjust the mud formulation and optimize its properties to minimize differential sticking issues.They have advanced the notion of oil-wetting actions by using pipes covered with materials that increase their attraction for oil and by using spotting oil that has been given an additional agent to make it more oil-wetting.
First, the amount of bentonite in the bentonite-water suspension was calculated; the results are shown in Table 2; as previously stated, Table 1 lists the ingredients used to make this drilling mud, which included bentonite clay, CMC, and PAC-LV.Table 3 lists its rheological characteristics, coefficient of friction, filtering qualities, and susceptibility to stick.The experiment's findings show that the rheological properties are satisfactory.Applying the Differential Sticking Tester at various times and filtration intervals, measuring the torque required to release a steel disc in contact with a filter cake.It enables the development of a filter cake and achieves the goal of sticking.After the extra mud has been cleared away and a spotting fluid has had time to absorb into the filter cake, its effectiveness is evaluated.
Tables 4 and 5 show how the mud emulsion affects the rheological properties, filtering qualities, coefficient of friction, and stickiness of the drilling fluids.This lubricant influences the properties of plastic viscosity, apparent viscosity (V), or yield strength.During this process, the gel loses some of its strength.This shows its compatibility with the drilling fluid.
Filtration loss decreased to 4.8 mL from 7. The extremely thin oil layer that forms when differential pressure is utilized may cause this.Both the friction coefficient and a notable reduction in the force needed to free the stuck ball.Torque is unnecessary to release the stuck ball if the friction coefficient is less than 0.05.These tests have shown that oil can reduce the likelihood of differential pipe sticking in water-based drilling fluids systems.When the data from Tables 4 and 5 are compared, it is clear that oil outperforms water at lower concentrations in preventing pipe sticking caused by water-based drilling fluid.While analyzing the data in Table .6,it is clear that the proportion of oil must be equal to or less than 3% in order to have no effect on the mud's qualities.The basic reason for choosing to study the rheological characteristics, plastic viscosity, yield point, filtration properties, fluid loss, and filter cake as the foundation for comparison is the importance of these parameters to the total drilling mud performance.The yield point (YP) gauges how drilling mud can carry cuttings from the annulus.Cuttings will be carried more efficiently by a fluid with a high YP than by one with a lower YP but comparable density since the fluid is not Newtonian.Additionally, YP and frictional pressure loss are closely related.It is critical to remember that overly high YP results in large pressure losses when the drilling mud is being circulated.Also, the findings show that adding oil to the mud can reduce the loss of filtrate, which may help to increase the likelihood that the differential stuck pipe will be released, as shown in Fig. 4.

5-Conclusions
This study highlights the importance of controlling the oil concentration in drilling mud to preserve the necessary rheological qualities.It is recommended that the oil concentration should not exceed 3% to ensure optimal drilling performance.By incorporating oil into the drilling mud, several advantages are observed.Firstly, adding oil effectively reduces the friction coefficient to less than 0.05, reducing the likelihood of pipe sticking.Lower friction coefficients contribute to more efficient drilling operations and reduce the possibility of differential stuck pipes.Furthermore, the reduced friction coefficient reduces the torque required to free a stuck ball, demonstrating the beneficial effect of oil in preventing pipe sticking issues.Moreover, bentonite clay in water-based mud has been identified as a factor that increases the risk of pipe sticking, particularly in high concentrations.
The observation of a significant friction coefficient with increased bentonite concentration supports this finding.Therefore, it is crucial to carefully manage the amount of bentonite clay in the drilling mud to mitigate the occurrence of differential stuck pipes.It is worth noting that the laboratory evaluation conducted in this research, which included torque measurements, provides valuable insights into the examination of differential stuck pipes.By analyzing and understanding the torque requirements during drilling operations, operators can better assess the likelihood of encountering pipe sticking issues and implement appropriate preventive measures.

Fig. 4 .
Fig.4.Self-fabricated set-up for the determination of sticking tendency.

Fig. 5 .
Fig.5.Comparison of the influence of oil on rheological properties

Table 2 .
Sticking tendency effect caused by bentonite concentration