Vallourec advanced drilling
with casing solutions
To optimize performance, drilling time and costs
1 – Drilling with casing application
Drilling with Casing (DWC), also called Casing-while-Drilling (CWD), consists in merging the casing running process within the drilling process. The DWC process allows casing strings (or liners) to be installed in a well during the hole making process where all, some, or none of the drilling tools required can be recovered after the casing reaches the required depth. Since there is a great variety of possible configurations for DWC systems, the casing (or liner) may or may not be rotated during the drilling process and the drilling tools may be integrated into the casing string or may be part of an assembly that extends below the casing shoe.
The Casing-While-Drilling concept is not new (United States Patent number 443,070 issued Dec. 16, 1890, introduced the concept of casing drilling to the world), but it gained momentum in the past 10 years as equipments developed to allow wider use of this technique and increase the benefits of DWC. Drilling with Casing has the following advantages compared to regular drilling:
– Enhance wellbore integrity by drilling with the casing, leading to a smear/plastering effect, which reduces fluid loss and cuttings volume. Because of the DWC side-load forces, the cuttings are pulverized in the narrow annulus, and as they travel towards the surface. Consequently, cuttings are smaller than with regular drilling. This smear effect is also due to smaller annular restriction and greater rotational velocity. The particles embed in the wellbore wall and cuttings help form a natural seal that is much more impermeable than a wall cake produced by mud additives alone.
– Drilling with Casing is a great tool to reduce NPT (Non Productive Time) and mitigate the unscheduled events while drilling. It is estimated that most drilling issues occur while tripping out drill pipe and running casing, when mud circulation is not possible. Hence, drilling with casing can provide significant cost savings. The industry estimates up to 1 billion dollar is lost every year, due to hole stability issues.
– Reduction of NPT is possible by eliminating extra trips and ensuring that the Casing is installed at TD from the first run. Tripping out the drill pipe and running the casing is no longer required when using Drilling with Casing as these operations are embedded in the drilling phase. Moreover, the running log can be eliminated when you choose to use a BHA including MWD/LWD.
Drilling with casing application is often split into 4 different levels, according to the complexity of the well design and the critical level of the interval to be drilled.
– LEVEL 1: The wellbore is already drilled with a regular drill pipe but the casing is rotated during casing running to ease operations. This includes operations such as rotating while cementing, casing reaming for ERD wells or shale gas wells.
– LEVEL 2: This is the most basic true drilling with casing and it combines OCTG casing for drilling and a top drive system. An OCTG casing is used to drill the hole and transmit the mechanical load to a drillable/disposable drill-bit used at the bottom of casing string. The wellbore is typically drilled in a single run and does not allow for the use of directional or logging tools. Accessories are installed along the casing string to limit vibrations and centralize the string for cementing after TD.
– LEVEL 3: This is an advanced drilling with casing that also combines OCTG casing with a top drive system. The BHA is retrievable during or after the drilling phase, before cementation begins. BHA can be retrieved through the drift of the casing, at will, at any moment during the drilling process thanks to a drillpipe or wireline. The casing is rotated at low RPM, and a motor in the Retrievable BHA allows the use of a RSS (Rotary Steerable System), MWD (Measurement while Drilling) and LWD (Logging while Drilling).
– LEVEL 4: This is an advanced Drilling with Casing that combines a top drive system, an OCTG casing for drilling phase as well as a liner hanger. BHA is often composed of an advanced retrievable BHA, similar to level 3.
2 – The challenges of drilling with casing for octg
In terms of OCTG, Drilling with Casing is challenging on four major levels, in addition to the challenges encountered in running a casing after drilling with a regular drill pipe:
1. Resistance to mechanical torque transmitted through the drilling string during the drilling phase;
2. Resistance to fatigue loading during drilling phase, as the OCTG casing is going through the various dogleg of the wellbore design;
3. Gas tightness required during drilling and production phase, after some fatigue resistance was partially consumed (induced fatigue can alter connection performance and its resistance to mechanical performance as well as gas tightness);
4. Gas tightness during production phase after high torque is required during drilling phase (Torque loads can alter the connection performance and its resistance to gas tightness).
The importance of these various challenges is related to the Drilling with Casing levels as summarized in table below. As drilling with casing is more widely used combined with challenging applications, such as production casing, assessing these four technical points through dedicated testing protocols is key.
One of the first performance expected from a T&C connector is its resistance to static loads as well as gas tightness under any static load combination (tension, bending, pressure…). The ISO 13679:2002 / API5C5 specification is the most adequate to assess this performance. Indeed, this norm presents all the recommended pratices to test casing and tubing connections. As shown on Figures below, the Von Mises Ellipse of a pipe (blue curve), is the yield strength limit under combined axial loads (tension / compression) and pressure loads (internal or external). The OCTG manufacturer then defines the working domain of the OCTG pipe (orange curve) and of the OCTG connector (green area) based on design rules and specifications (API5C3). Finally, test load points (in yellow) are determined based on the connector’s limits for full-scale testing.
Once the test load points are determined, the test cycles are defined based on application severity. 4 levels are defined from the less stringent (CAL I) to the most stringent (CAL IV). CAL I level is generally dedicated to pipe used for liquid service. CAL IV is mainly dedicated to pipes used for gas service in direct contact with the production fluid (tubing and production casing), where thermal cycles are expected.
However, the fatigue resistance of OCTG products is not normalized as gas tightness evaluation is through ISO 13679. Moreover, the combination of such mechanical loads with fatigue resistance is not really standardized, and neither is the way to determine fatigue resistance of OCTG products. It is therefore imperative for the OCTG manufacturer to set up an adequate testing procedure to evaluate gas tightness after fatigue damage was consumed within the OCTG product.
3 – Vallourec offer for drilling with casing
DEFINITION OF TEST PROTOCOL DEDICATED TO DRILLING WITH CASING
Fatigue resistance determination
In addition to the previously mentioned ISO 13679, Vallourec has acquired significant knowledge in establishing the fatigue resistance of its OCTG products. This fatigue resistance is evaluated through physical tests, in a vibrating bench that can virtually replicate the vibrations and dynamic loads encountered during drilling. This test methodology considers statistical analysis inherent to fatigue phenomenon together with FEA analysis and product line approach to derive fatigue performance of every single size of each VAM® product line to be used for a drilling with casing application. An example of fatigue performance is shown on the chart below. The blue curve of fatigue resistance is determined by the statistical analysis of each of the blue points obtained through the physical tests in the vibrating bench.
Gas tightness resistance after fatigue damage
Following the determination of the fatigue resistance of the product, Vallourec replicates the dynamic drilling loads on an actual sample to check the influence of fatigue damage on product performance. As each well is unique, Vallourec uses a standardized and conservative approach to evaluate the compatibility of the VAM® product with all wells.
It is generally admitted that service companies and end-users will not exceed 50% of the fatigue life of the OCTG product consumed during a drilling with casing job. This is where we must consider safety as a key factor for this operation. Consequently, Vallourec consumes 50% of the fatigue life of the product on a vibrating bench similar to the one used to test fatigue resistance (the orange curve of the chart). The sample is specifically designed to be compatible with a sealability bench (illustration).
The latter is used after 50% fatigue damage was generated into the product to check sealability performance is not altered in the casing during production (gas tightness and mechanical performance).
DETERMINATION OF VALLOUREC OCTG PRODUCTS PERFORMANCE FOR DWC
VAM® 21 is one of the latest products designed by Vallourec with enhanced performances compared to the previous generation of connection such as VAM® TOP. VAM® 21 surpasses the highest level of gas tightness required by ISO 13679 CAL IV. This demonstrates its superior performance for complex applications, such as production casing in challenging HPHT environments.
In addition, VAM® 21 was also designed to withstand superior torque. Indeed, the torque capability was significantly improved compared to the previous generation of OCTG products, namely VAM® TOP.
In order to demonstrates its suitability to the most advanced drilling with casing applications, VAM® 21 was tested in terms of fatigue to evaluate its resistance dynamic loads, typical of drilling with casing applications. The test protocol described above was carried out to evaluate fatigue performance.
Finally, VAM® 21 was also tested for gas tightness, according to ISO 13679, after 50% of the fatigue damage was introduced in the connection, according the test protocol. Test results proved outstanding, with advanced gas tightness resistance equivalent to the highest level in ISO 13679 (i.e. CAL IV). All the combined results prove the superior resistance of VAM® 21 to all static and dynamic loading.
This methodology is now generalized to all VAM® products dedicated to drilling with casing application. Vallourec is now capable to derive fatigue performance for each of the product listed below and validate its suitability for the client’s needs and design.
EVALUATION OF VALLOUREC PRODUCTS FOR DWC APPLICATIONS
Once all the fatigue data required within this document is available, one of the objectives is to provide end-user with an analysis of the foreseen drilling phase and compare it with the performances of the product:
– The Torque and Drag analysis performed by end-users is compared to the static performances of the product (Torque, Tension, Pressure, Bending…) determined by the ISO 13679 test. Vallourec then issues a performance data sheet and recommendations for the specific well design that will be drilled.
– The dynamic analysis of the drilling phase is estimated to calculate the amount of fatigue consumed during the drilling phase. The fatigue consumption is then compared to the performance of the product as shown below.