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Senin, 21 Januari 2019

PETROLEUM WELL COMPLETION OVERVIEW


PETROLEUM WELL COMPLETION OVERVIEW

WELL COMPLETION DEFINITION
Well completion means preparing the well for production, of course well completion is worded only when the well have sufficient amount of oil and gas to be commercially viable. That is why data from all the evaluations and tests is so important.

Now with probable positive evaluations, we are ready to complete the open hole, part of the well. These open holes, where we conducted our wire line tests and coring can now be cased and cemented to become a closed Cased Hole. When we talk about running casing in well completion, we are only referring to the casing the zone or zones of interest in the open hole. These casing strings are referred to as production casing it is sometimes easy to confuse the function of production casing, with those of surface intermediate casing.


Well Completion - Well Casing

WELL CASING
It can be explained that surface casing for example is the first casing string to be run when the well is first drill, as the name imply the surface casing, since it's the top part of the well and his attached to the well head, it's primary function is to protect the groundwater formations from contamination.  In deeper well a second type called an intermediate casing is running and cemented, intermediate casing is required, its primary function is to protect and support the hole above the zone or zones of interest. Surface casing and if needed intermediate casing strings are install during drilling on all wells regardless of whether they are commercially viable or not.  The production casing strings on the other hand are only run when the well shows problems of becoming a producing oil well, running and cementing this casing segment are part of the first steps in well completion.

Well Casing – Surface Casing Function

Well Casing – Intermediate Function

Well casing - Production Casing Function

Once the production casing is run, cemented and attached to the surface, and the intermediate casing string at the wellhead, these casing form what is known as a close hole or cased hole. This hole from the top to the bottom is now sealed off from the natural fluids and solids that exist in the sub surface.

. Well completion – Open Hole

Well completion – Cased Hole

Well Completion Procedure
Well completion however, involves more than running casing and sealing the hole, to complete a well after the casing running and cemented, the following procedures can be performed:

1.    Perforation
Once the production casing in place in the zones of interest, the casing then perforated, which means blast through the casing and the cement deep into the formation.

2.    Stimulation
After perforating the zone is stimulated, so that inadequate production or flow rate of the hydrocarbons can be attained.

3.    Gravel packed
If its needed the zone can also be gravel packed to stop sand production

4.    Tubing, packers, and a christmas tree
Finally the well is equipped with tubing, packers and a christmas tree to control the flow of fluids to the surface.

Well completion – Perforation

Well completion – Stimulation

Well completion – Gravel Packed

Well completion – Tubing, Packers, X-mas tree

Before we described each of the above procedures, to finalize well completion in more detail, we take a minute to explain one action is taken when are well is not commercially viable. When a well stated no zones of interest or has a little commercial viability it is declared a dry hole. This well would be permanently plug, then abandoned call P&A, for plugged in and abandoned, this procedure requires that several cement plugs be placed in the hole to seal it.

Well completion – Plug & Abandoned (P&A)

As we know that wildcat wells, wells in areas where no one has drill before are more likely to be dry holes. The industry figures suggest that as many as seventy five percent (75%) of all drilled wildcat wells are dry. P&A procedures therefore, can become quite routine in wildcat areas, in this book then would pertain to the procedures and their functions used in well completion. Although already mentioned well again present the three types of casing string and explain their functions, in addition we illustrate the different procedures and the specific equipment needed to ready the well for production.

Specifically we present a brief summary of casing design, casing equipment, cement operation, Perforation, well stimulation, sand control along with the file equipment needed to prepare a well for production.

Well completion – summary

Well Casing Function
Let’s start with the four main functions of the surface, intermediate, and production casing strings with their cement sheet or covers. First, all three of the different types of casing protect the whole from the mud, that's preventing soft formations of shale from growing water out of the mud which then can cause the shale to swell and blocked or impede the drilling operations.
Well Casing Function

In addition casings prevent surface sediments and other unconsolidated formations from being eroded by the mud system. Second function relates all to surface casing, this casing protect near surface freshwater zones from contamination by deeper salt water zones. we sure people rely on these freshwater aquifer, polluting these aquifer is  usually prohibited by law or can create serious environmental issues. Third all three types of casing the surface, the intermediate, and the production casing provide a smooth entryway and path for running tools in and out of the hole. Finally in production casing, its surroundings cement sheet isolates down the hole zones, so that the different zones can more easily be produce separately.

Now let's examined the standard procedures involve the closing and open hole. The first step in closing and open hole is to drive the production casing string to the bottom of the hole. The casing string is permanently set in the well by pouring concrete into the annular space between the casing and the wall or the hole. let me point out here,  that because the drilling string must be able to fish comfortably inside the casing string, the casing string pipe must be large enough to allow the drilling string pipe fit inside it.  Like the drilling string, the three types of casing strings consist the multiple joints but of larger diameter pipe that is screwed together one join out of time as it is inserted to the bottom of the hole at total depth (TD).

Well Casing for Closing Open Hole

Well Casing in Drilling Process
Casing strings are run and cemented into place as the well as drilled deeper to protect the hole from further exposure to the circulating mud. The exact number of strings depends on the depth of the well, the relative stability of the formation penetrated, and the characteristic of the drilling mud. As discussed earlier, as each casing string is run it is run inside the previous string that was slightly larger. Conversely the diameter of each new string will be smaller than the one it fits into as the casing is run deeper. Imagine those sets of plastic balls that you can buy at any supermarket where the smaller bowl fits inside a larger one which fits inside and even larger one until you get to the biggest bowl with all the small bowl fitted neatly inside. there for, to be sure that the casing string fits together properly, it is imperative that the casing program preplanned before drilling begin so that the surface hole and pipe can be large enough to accommodate all the strings that will be push through it.  Keep in mind that the final string must be small enough to fit through all casing joints while still being large enough to allow oil or gas to flow adequately for its capacity.

Number of Drilling & Casing String

When inserting the initial casing string, the drilling operation, drills their large diameter surface hole to unconsolidated surface material and protects sources of fresh water in the nearby water table, called the surface casing string. It is usually a few hundred feet and runs to the bottom of the whole at the beginning when drilling first begin.
 Surface Casing

Once in place cement slurry is then pump down the inside of the pipe and circulated up the backside annular space between the casing and hole.

Running Surface Casing

Once the surface casing is in place, drilling resumed for shallow wells the surface casing maybe all that is required before initializing the production casing. For deeper wells or where the formation becomes unstable because of long contact with the mud and intermediate casing string maybe necessary.

A very deep hole may require two or three intermediate strings. To establish and intermediate casing the surface casing must be drilled through using it smaller bit that fits inside the surface casing pipe. The drillable shoe on the surface string and the cement in the bottom of the hole is easily penetrated. Once the slopping zone is penetrated the drill strings is pull and intermediate casing string is run to the existing bottom and then cemented into place.

When using an intermediate casing it is important that this cement rises high enough in the annulus to reach and tie into the cement in the surface casing pipe. It is essential to provide an unbroken cement sheet that covers the entire length of the hole, these steps or repeated as each success of string of the intermediate casing is hung from the wellhead at the surface. Finally the wellhead access is sealed, to seal off the annulus at the end of the casing string, both the surface and intermediate of casing strings are installed while drilling continues to total depth.

Once in the zone of interest that has been identified, it is not cased yet, this section of the well is referred to as open hole. Basically it is the length of the hole from the surface or intermediate casing strings to TD, as we know about open hole, that open hole well logs and identify the lithology, measure permeability porosity, the reservoir thickness, and fluid saturation are finalized. Once the potentially commercial viable well is confirmed, this section of the hole is then cased and completed.

Open Hole Logging

Cased and Perforated

Then the production casing, long string or oil string, the string is set through the producing zone, and cemented, ensuring that it is tied to the string above so that there is a continuous sheet of pipe and cement from bottom to top. Later this casing and cement will be perforated to get access to the producing zone.


For further read, you may get the book from amazon.

PETROLEUM WELL COMPLETION OVERVIEW

https://www.amazon.com/PETROLEUM-WELL-COMPLETION-OVERVIEW-1/dp/1792195575


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