The Using of Unconventional Method depending on Well Power in the Mishrif Formation to Release Differential Stuck Pipe, Nahr Umr Oil Field, Southern Iraq

Abstract


Introduction
In southeast Iraq, the Mishrif formation consists of major carbonate reservoirs, with 32 structures containing oil (Awadeesian et al., 2019).Rumaila, West Qurna, Zubair, Majnoon, and Nahr Umr oilfields have the highest accumulations of oil as well as large north-south trending anticline structures.(Aqrawi et al., 2010).According to Mahdi (2020) facies are characteristics that have historical, structural, and synthetic origins that are modified and accumulated within depositional settings as a result of deposition processes.Various physical characteristics of carbonate sediments and rocks can be attributed to their different deposition and diagensis processes (Al-Baldawi, 2020).
The issue of the drilling string losing its capacity to rotate and move up or down is known as stuck pipe in general.It is crucial to remember that a stuck pipe is a common issue that occurs about 25% of the time in the entire non-productive time (NPT) (Belaskie et al., 1994;Siruvuri et al. 2006).Because of this, it is not surprising that people and companies are attempting to develop suitable methods for dramatically reducing its frequency and the negative outcomes.Around 50% of the time, pipe sticking occurs during tripping, 10% when bottom drilling, 20% when operating the pipe at a connection and reaming, and 20% during other operations (Belaskie et al., 1994).
Many studies have been done in order to find the appropriate methods to prevent and treat the differential stuck pipe.Siruvuri et al. (2006) presented a neural network method for identifying the causes of the differential pipe stuck problem.The strategy was more of a predictive tool, according to the authors.As they stated, it is possible to estimate the stuck pipe both before and during drilling.Additionally, it was shown that the trained neural network could automatically identify the parameters that might be the cause of the stuck pipe issue.Amina and Al-Haleem (2018) conducted a study to analyze the occurrences of the differential stuck pipe in the Khabaz Oilfield.To investigate the issue of stuck pipes in this oilfield, well Khabaz-34 was chosen.The graphing analysis program Easy View was used to analyze stuck pipe incidents.Eventually, they suggested using the right kind of drilling mud with the right rheology characteristics and optimizing the casing seat design to minimize the likelihood of a stuck pipe.Al-Mahdawi and Saad (2018) used the LTLP filter press to assess the effectiveness of silicon oxide nanoparticles.They discovered that increasing the concentration of nanoparticles causes the amount of filtrate to decrease.Amina and Al-Haleem (2018) conducted a study to analyze the occurrences of the stuck pipe in Khabaz Oilfield.To investigate the issue of stuck pipes in this oilfield, well Khabaz-34 was chosen.The graphing analysis program Easy View was used to analyze stuck pipe incidents.Eventually, they suggested using the right kind of drilling mud with the right rheology characteristics and optimizing the casing seat design to minimize the likelihood of a stuck pipe.Abdul Aziz and Abdul Hussein (2021) developed correlations for evaluating mechanical rock characteristics in properties in Mishrif formation using labortary measurments.Fadhil and Al-Haleem (2022) presented that Tanuma and Zubair formations' shale cuttings were described using a stereomicroscope, and the shale structure was observed using a scanning electron microscope.Determined that the specified drilling mud for Tanuma shale can be used to drill Zubair shale and that the reverse is incorrect.They also reached the conclusion that the shale rocks are scattered in fresh water and can become stable by utilizing inorganic additives (KCl).Issa and Ayad Al-Haleem (2022) presented mechanisms of pipe sticking and they have mainly focused on mechanical pipe stuck in selecting studies.The study aimed to identify stuck pipe problem in Zubair oil field by choosing four wells.Finally, they concluded that a higher flow rate need to prevent mechanical pipe sticking and the values of other parameters, such as yield point (YP) and plastic viscosity (PV), drill string rotation speed, penetration rate, and cutting density, have an impact on flow rate values.
In this study, it may used the unconventional method depending on well power in Mishrif formation to release stuck pipe and design the appropriate drilling mud weight to avoid this problem in the future and finally comparing it with the conventional method in relation to the time and cost.
The Nahr Umr oil field is considered one of the largest fields in southern of Iraq.Wells drilled in this field are related to the risk of differential stuck pipe, especially when the well driling through Hartha and Umm Er Radhuma formations.

Conventional Methods
To calculate the free point depth during the pipe sticking problem, the length of the free pipe has to be determined initially.The free pipe depth can be measured by the available data and using the following equation (Lyons et al., 2015).

Calculation steps
The following steps can be used to summarize this section: • Gather the necessary wells data from the specific field.
• Using stuck table to identify stuck pipe mechanism.• By summation of all points of surface indication we can diagnose the type of stuck and react as per recovery techniques for each type of stuck.• After identify the stuck mechanism is differential, apply maximum flow rate as possible • Calculate stuck pipe depth The stuck-pipe problem consists of several layers of protocols to remove the obstacle.Sometimes there will be enough tools to free the pipe, but the pipe cannot be freed at a certain point unless the free point is known.To know the free point, based on the known parameter, is calculated ( DeGeare, 2014).
• Spotting fluid as stuck breaker to reduce the contact area between stuck string and mud cake and then pull the string with allowable over pull.

Unconventional method
This method will use after the conventional methods failed to release the stuck pipe.The principle of this method that decrease hydrostatic pressure and depend on well power in order to reduce the filtration invasion, coefficient friction and decrease the stuck contact area that may lead to treat the stuck pipe and then reduce the force need to release the stuck pipe.The unconventional method can be applied in all Iraqi fields and can be used in all formations if do not contain gas.Finally, The steps and calculations of the unconventional method are easy.

The Problem
While drilling the 12 1/4" hole at depth 2215 m in Mishrif formation with the rate of penetration (ROP) (averaging 1.5 m/hr), and the operator had to apply higher weight on bit (WOB) and ROP while drilling.Once pump pressure increases the supervisor used to pick up off bottom and to circulate for 10-15 minutes to make sure that the drilled cuttings circulated and moved away from the annulus then gently washing back to continue drilling again with the same parameters.
Continuous drilling formation to depth 2263 with the increase in filtrate and mud losses, they decided to pull out the string for condition mud properties and treat the losses, during pulling out at depth 1834 m stuck pipe occur (Hartha formation).After that stuck pipe happened and with mud return but cannot moving the string up or down.
As shown in Fig. 1 mud pump pressure decrease was low because the mud cake formed in the permeable zone which cause increase in the filtrate.This problem must treat by using material such carboxy methyl cellulose (CMC ( and polyanionic cellulose (PAC) before greater and become difficult to treat.

Conventional method
After identified differential stuck pipe mechanism by stuck chart, the procedure to free differential stuck pipe is: • Apply maximum flow rate as much as possible and maximum flow rate is 1780 L/min estimated as following:

Depth (m)
• Stuck pipe depth is 1771 m by using equation (1) as showing in Table5: • Work string up with over pull gradually from 10 to 25 ton with no success.
• After the previous trying failed to free the stuck, jar down used to release stuck pipe with (over pull 60 ton/slack off 30 ton).This operation repeated many times with no success.
• Spotting 7 m3 of a friction reducing fluid (stuck breaker + diesel) and displaced by 2 m 3 water then 20 m 3 mud within the stuck zone to decrease the contact area between the stuck pipe and formation and waiting for 8 hour to activate spotted fluid and then pull the string with (over pull 55 ton/slack off 25) with no progress.

Unconventional method
• Stuck pipe occurred in Hartha formation and will use this method to release the stuck pipe after the conventional method failed.By adding 25 m 3 of water for decreasing the mud weight from 1.3 to 1.26.The purpose of this step is to decrease the contact area in the stuck zone and decrease the invasion of filtration into formation by well power.• Work string up and down with over pull 27 ton.The string succeed to release from stuck zone and pull out to inside previous casing to control the mud and then pull the string out the hole to check if there any lost pipe. the cost of the unconventional method less than the conventional method because it spends less time, the conventional method include many steps to release the stuck which spend more time while the unconventional method has the ability to release the differential stuck pipe quickly (Figs.2and 3).

Conclusions
By utilization of early warning signs charts, Monitoring torque and drag and analyzing them, accordingly; taking all precautions and actions if anything was abnormal and make fast and safe connection timing since most of the pipe sticking occurs at that stage.In case getting stuck, first to diagnose the cause and type of stuck then following all pipe sticking procedures starting from going to the opposite direction of the stuck, Practice effective jarring down and applying toque and jarring up, manipulate mud properties, then spotting effective releasing agents in stages starting with surfactants ending with last stage to be HCl and other strong acids.If none of above steps succeeded, can use the unconventional method if there oil and salt water only and do not use with gas or sulpher water because

Cost ($)
them are highly flammable and toxic.The unconventional method cheaper than the conventional method because it spent less time that may lead to less cost.The appropriate mud weight to drilling hole (12 1/4") in order to avoid the differential stuck pipe problem is )1.27 gm/cc ( because high mud weight formed the thick mud cake through permeable formation that can lead to the differential stuck pipe.Coefficient friction did not change with changing differential pressure and increase or decrease with changes in mud composition.

Table . 1
.Table to identify type of stuck pipe

Table 2 )
Pump pressure versus depthMud weight is high which lead to form the mud cake in permeable zone and increase the probability of differential stuck pipe (Table3.Pressures values in the Mishrif Formation

Table 4 .
Maximum flow rate

Table 5 .
Estimating of stuck pipe depth