CASING REPAIR IN OIL WELLS

During the productive life of wells has been presented injury break in the intermediate and production casing, caused mainly by corrosion, wear travel and pipe rotation during workovers and fishing, this situation has caused production of unwanted fluids and in some cases affecting sand pumping system electrosumergible production, prompting the closure of loss of production wells and in some cases loss of the well.

Due to the magnitude of the problem, this paper describes the application of techniques Tie Back, Tie Back Short, Casing Patch, Scab Liner, special packaging and insulation cement works, used successfully in the repair and rehabilitation casing of wells that have possible to restore the well production casing closed due to rupture of Lot 8 in the northern jungles of Peru operated by the CIA Pluspetrol.

It analyzes the main causes of damage to the casing and how to minimize it, describes the techniques used to detect and assess the damage to the casing, determines the factors for the technical-economic assessment shows the operating sequence and the use of special tools conditioning and repair of casing from wells operated taking into account the special conditions of each well, which allowed production to restore and extend the productive life of wells.

INTRODUCTION
Producing wells in the fields operated by Pluspetrol have electrosumergible production system with pumps installed to 2,200 m. depth, the depth of installation are depending on the productivity rates of sand production and the extraction volumes in order to maintain adequate levels of submergence of the pumps.

The completion of the wells is performed with intermediate casing 9 5 / 8 «to average depths of 2,500 m. and production laina 7 «to depths of 3,200 meters. These wells are mostly aimed at maintaining the inclination in the section of casing 9 5 / 8 «. These conditions of the production system and well geometry among others, are those who have the highest incidence of damage to the casing process, occurring mostly this problem in the casing 9 5 / 8 «.

FACTORS THAT AFFECT THE INTERMEDIATE CASING DAMAGE OF 9 5 / 8 «

DESIGN OF WELL.
The geographical conditions of the Peruvian Amazon are expensive to build platforms, communication routes and logistical support as a vertical well is drilled and led 3-5 wells from a single platform with spacing of 400-1000 m. The wells drilled are targeted like «S» and Slant, depending on the horizontal distance between the coordinates of surface and ground, stability for the perforated drainage area of training to produce among others.

The average depth of wells tubing is the tubing surface
conductive 20 «up to 50 m., surface casing 13 3 / 8» up to 500 m. and intermediate casing 9 5 / 8 «up to 2500 m. and this section has presented the greatest damage by corrosion. The completion of the wells is performed with production laina 7 «casing in some cases with 7» to surface.

Well geometry.
Approximately 50% of wells drilled in the forest are directed mainly of type «S». The onset of the deviation (kick off point) is performed at vertical depths of 50 m. 150 m. The gradient of increasing deviation angle used in the wells is 2 ° / 30 m. and the maximum vertical angle of 18 ° to 30 °. The fall of the angle is performed in 1300 m. 1600 m. with a falling gradient of 1 / 30 m. Mostly, the points of direction change increases the friction between the casing and tubing. In Diagram No. 1 shows the typical design of a reservoir type «S» in the area of Corrientes – Pavayacu.

METALLURGY OF CASING.
The strength of the casing corrosion depend on the type of microstructure obtained by heat treatment and chemical composition of steel. In some cases the intermediate casing corrosion may have been motivated by the use of casing that does not comply with these requirements.

FRICTION FOR TRAVEL AND ROTATION OF PIPE.
The friction caused by contact with the casing pipe during travel and work wherever necessary to rotate the pipe (fishing, drilling plugs, clean sand, etc) generate wear damage to the casing.

WORK OF FISHERIES AND GRINDING.
Efforts to support the casing at points of fishing and drilling permanent closures
cause wear. Increases damage when cut or drilled cap remains are not recovered in due course, these remains are not recovered with the movement because of its weight and volume (annular space between DC 4 3 / 4 «casing and 7″ ID 6.19 » ), necessitating the use of recuperators fracmentos baskets as junk basket or baskets of reverse circulation.

BUBBLE POINT SYSTEM FOR PRODUCTION.
Corrosion Failures occur from bubble point to surface at this point the CO2 is separated from the oil and begins to dissolve in the salt water carbonic acid that corrodes the metal.

The low level of submergence of electric submersible pumps causes release of CO2. By
example, the bubble pressure of crude oils produced in the Member’s Current Deposit Cecropia is 760psi to 460psi and Member Pona.

BY COLLAPSE OF FLUID LOW.
Low fluid intake causes the sands productive use of electric submersible pumps low extraction rate under submergence level, which must be installed at depths of up to 2100 m. It is a condition to cause breakdown in the casing 9 5 / 8 «differential pressure due to hydrostatic pressure of training, a situation aggravated when there is a good cementing the casing.

Presence of corrosive fluids.
The reservoir rocks are mainly sandstones and clean your setup is possible that the corrosive agent comes of it. An analysis of the oil produced has low sulfur salts 0.35% and 3.25 PTB.

The high content of CO2 (4.05% Mol) obtained from gas analysis Chonta Formation indicates that the source is this corrosive fluid. The percentage of CO2 influences the corrosive property of the water acting on the pH, the greater the amount of CO2 in the gas or water, the pH will be lower and the water more corrosive. The formation water records containing Fe +2 in the order of 100ppm, chlorides (110,000 ppm) and total dissolved solids (144,000 ppm). The high court of produced formation water leads to increased wetted surface favoring the corrosion process

IMPROPER cementation.
Poor cementing casing through entrapment causes of drilling mud, which by staying in contact with reactive shales can change the pH of the sludge by electromechanical action, creating a corrosive environment against the outer wall of the casing. The pH of the sludge is greater than 9 and does not contain soluble salts or organic acids. A good concrete wall protects the outer wall of the casing.

DAMAGE ASSESSMENT AND DETERMINATION
Initially the damage intermediate casing 9 5 / 8 «change is detected by physical and chemical properties of produced formation water pumping system with electrosumergible. To determine specifically the area or areas in poor condition are tested for admission to packaging; records corrosion, temperature, density, among others, depending on the conditions of each well.

REGISTRATION OF CORROSION.
It is a record that provides accurate information of the damaged area and a full assessment of the state of the casing.

Temperature records.
With this record only gets information from the damaged area due to change in the gradient
fluid intake, mostly used in wells that have produced surface flow of the damaged area.

Density log.
Measurement of the area damaged by changes in the density of fluid produced.

TIGHTNESS TESTS WITH PACKAGING.
It insulates the production and test the tightness of the casing pipe or linings selectively reducing the test interval has admitted. May be the case of damage to the casing with a low intake.

TESTS OF PRODUCED WATER SALINITY.
The determination of salinity of the water produced by comparison of characteristic patterns
generated from the ion content lets us know the changes for different water ingress to the area of production.

EVALUATION FACTORS FOR TECHNICAL – ECONOMIC
To evaluate the feasibility of a repair job intermediate casing is taken into account the following factors:

PETROLEUM RESERVES.
The volume of existing oil barrels and recoverable within a reservoir. If reserves of the well justify the investment of a temporary or permanent repair.

SIZE AND LOCATION OF THE DAMAGE.
The magnitude of the damage if timely or general corrosion and its location (depth range of casing damaged), for determining the type of repair to make.

DESIGN AND WELL completion.
The quality of cement work and completion with intermediate casing 9 5 / 8 «liner 7» production casing 7 «or 5 1 / 2» to surface are decisive factors to select the appropriate decreparación technique.

PRODUCTION SYSTEM TO BE USED.
The productivity index of the productive formation of the well fluid level allows the design of artificial lift equipment electrosumergible, installation depth and rate of extraction.

CONDITIONING OF WELL.
The conditioning of the well depends mainly on the repair to make, how much damage, stability of unprotected training section for casing, cementing and completion of the well casing.

The calibration of the well casing before lowering repair tools or permanent installation is very important, depending on the status of the well tools may be used for correction and calibration as the roller casing, water melon, melon string, taper mill, scraper, among others. The fluid used in the repair depends on the state of the well, and densified fluids used in pits viscosificados present instability of the formation of unprotected section with casing.

REPAIR TECHNIQUES.
Currently a large variety of tools and techniques for repair of casing, due to the production system employed electrocentrífugo pumping wells and completion of repair techniques we applied casing 9 5 / 8 «which have allowed us to restore production well stopped by this problem, improve the mechanical condition and ensure business continuity in them. We describe the techniques used successfully in our wells.

TIE BACK – WELL – 81D
The repair technique is applied with Tie Back in wells with production laina. Is to connect the casing hanger and extending to surface laina, cementing the annulus between the casing and intermediate casing installed. This technique can cover the entire stretch of intermediate casing. When applying this technique to be installed on the wellhead for a reel casing hanger installed. This fix does not limit the depth of installation of electric submersible pumps.

SHORT TIE BACK – WELL 32XC
Repair with Tie Back Short applies laina production wells. Is to connect
laina casing hanger and to extend it to cover the damaged areas by installing a new hanger laina, cementing the annulus between the casing and intermediate casing installed. This technique is applied when the damaged area of the intermediate casing is near the top of laina and there is no limitation on the depth of installation of electric submersible pumps.

SCAB LINER / LINER CASING PACKER WITH 7 «WITH ISOLATION AND PACKAGING – WELL 15XCD
The Scab Liner / Liner Packer is to install a smaller diameter casing covering the range of intermediate casing damaged, the installed casing is fitted with hydraulic seals, the same as isolate the damaged area. You need to install a guide at the top and bottom of this facility to allow the passage of tools and electric submersible pumps. This type of repair does not limit the depth of installation of electric submersible pumps.

We used hydraulic seals to isolate the damaged areas where the depth of sitting on the packages are not limiting the depth of installation of electric submersible pumps.

CASING PATCH – WELL 16XCD
Casing Patch The technique is applied in wells where the casing is in poor bonding, consists of removing the casing into disrepair, and replace it with new casing. The union between the well casing and the casing is installed through the casing patch lead seal, the annulus can be cemented to surface. When applying this technique to be installed on the wellhead for a reel casing hanger installed. This fix does not limit the depth of installation of electric submersible pumps.

CONCLUSIONS AND RECOMMENDATIONS.
To solve the problem and restore the damaged casing production wells have applied various techniques. For the application of these techniques describes the background of the wells were applied and the procedure allowed a significant success. Of all the techniques applied, which guarantees the best mechanical condition of the casing and the well operational continuity is the installation of casing Tie Back with 7 «to surface with cement in the annulus. The wear on the intermediate casing areas inclinadión change caused by friction during the rotation of the pipe in the drilling of EZ caps and fishing operations can be reduced with the use of engines in the background.

The use of protective rubber pipe reconditioning friction reduces wear on the inside wall lining during travel through the work of reconditioning. In milling operations, the metal remains to be causing damage caps trapped between the production casing 7 «and the drill collar 4 3 / 4» OD. This damage is reduced using metal tools such recuperative junk remains junk basket basket and reverse circulation.

Use standard casing resists corrosion and make a good primary cement to surface. Continue to evaluate the production system electrosumergible dual hydraulic packing installed in wells with low productivity index so as to avoid the collapse of casing for low submergence, since the packaging allows you to maintain the annular space filled with fluid. Chemical injection for corrosion protection inside and outside wall of the casing.