The by equipped barrels for physical examination [3].

The largest and the most significant part of investment for an oil company is drilling section. Drilling rigs are the biggest part of drilling section which is provided with a contemporary hoisting system to move the string 1. An efficient and fully documented well design is needed and an engineered plan is drafted to ensure that the rig team has all the necessary information to fulfill the work safely. A well is created by drilling a hole between 5 and 30 inches in diameter with a rig which rotates a drill bit. when the hole is drilled, a steel pipe which called casing, slightly smaller than the hole is inserted in the well and supported with cement. This casing provides structural completeness for the newly drilled wellbore. Furthermore, the casing is used to prevent the drilled hole from collapsing. Inside the casing, a production tube is tripped in. After drilling the well and setting the casing, the well must be ‘completed’. Completion is a process which is utilized to prepared the well to produce petroleum 2.

CORING is the term applied to the operation through which proportionally large samples in comparison with the normal size of the drilling cuttings of reservoir rock are taken from their original place with special bits. Then they are transferred to the surface by equipped barrels for physical examination 3. Core analysis has turned into a way to know what is going to occur in the reservoir properties. Engineering core analysis properly provides a direct sense of these reservoir rock properties and is an essential step in formation evaluations. Although coring presents exact information about reservoir rock, having a small scale is the reason for some laboratory errors. In this regards, fundamental core analysis measurements are unchanged, but advanced tools provide the ability to examine reservoir conditions and acquire simultaneous measurements of reservoir properties 3.

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Normally, the most brilliant information derived from the coring operation consists of:

v  Porosity which is a measure of the fluid-carrying capacity of the formation or how much space occupied by fluids.

v  Permeability which indicates at what rates the formation fluids will be able to flow.

v  Water saturation which tells us about the percentages of the reservoir water 4.

v  Hydrocarbon saturation which includes the relative percentages of oil and gas.

Cores are also obtained for a variety of other reasons including geological studies, studies of fracture patterns in fractured formations and studies of formations in order to reach better well completion. So the aim of this study is calculating the friction forces of core jamming and decreasing the number of reasons which slows down the speed of operation 5.

 

Core jamming is one of the most fundamental challenges of coring operations. So that it stops the operation and it causes to trip the drilling pipes out from the well even if the inner tube is not full of core. Many corporations are carrying out coring operations and large investment is used in this industry. Sometimes core jamming, posting drilling operations for days and increases the rig time. A lot of research has been done in this field to identify the causes of the core jamming and a solution to it. With all of these efforts, there is no proper solution to the problem but tools are also designed such as: 1.       Jam TeQ core jam mitigation system which is presented by NOV company. This system gives the operator the ability to stay on bottom and take core without interruptions 6. 2.       The patent with the title of ANTI-JAMMING CORE BARRELS where a rotary jar located inside the inner barrel. At the time of core jamming, by using some strokes in the inner barrel, it releases the jam 7. 3.       Another system which is used in the industry is the telescopic system that fixes up to three jams and It is made of stainless steel with a length limit of 9 meters. This system has been tested in one of Pakistan’s exploratory fields, the name of this system is JAMBUSTER 8.  

THEORY

 

BACKGROUND OF PROBLEM

Because of high cost of drilling operations, it is essential to develop an accurate prediction of drill performance and drilling rate to estimate the time needed to complete a well. Previous studies show that a small portion of the total drilling time is spent on actual rock cutting in the wall by the bit, and the rest is the downtime components which include tripping the rods in and out of the well 9. Core interval length can be compromised if it is jammed. But this is more significant and something which is challenging in the case of exploratory wells due to firm coring requirements of a certain interval of formation. This data is especially momentous for further core studies. So, successive and multiple coring runs are required with conventional system. This not only eventuates to additional time and cost loss for the operator but also keeps the hole open for more days which results more invasion of mud filtrate to the formation 8. 

 

 

CASE STUDY (BANGESTAN GROUP)

It’s the title which is given to a geological formations group in Zagros from the era of Albian to Campanian which consists of a sedimentary cycle of Kazhdomi, Sarvak, Soorgah and Ilam formations. Series of these formations are named Bangestan group which is taken from Bangestan Mountain in the north of Behbahan city. Crichton predicates the name of Bangestan lime to the Middle Cretaceous limestone. James and wynd upgraded the name to the Bangestan Group and included Kazhdumi, Sarvak, Soorgah and Ilam formations. They counted Sarvak and Kazhdumi as a sedimentary cycle and justified positing the Kazhdumi Formation in Bangestan Group 10.