From the Designing

Cementing operations represent one of the more crucial aspects regarding well integrity. Despite the vast amount of research and the large number of operations throughout the years, well integrity problems, during and after cementing jobs, is something the industry still faces. These problems have been experienced by the petroleum industry globally and can occur at any moment of the well’s life cycle. Well integrity issues have been categorized according to the moment at which they happen:

  1. During the cement displacement in the wellbore.
  2. After the cement placement.
  3. After the cement has been cured.

The first category may result in very serious well-control problems, including blowouts. During the period between 1992 and 2006, the leading cause for blowouts was cementing. These problems usually occur because of improper design of the cementing operations due to hydrostatic pressure of the cement slurries, failure when mixing the slurries to obtain the desire density, and lost circulation during the cement displacement.

The second category is normally associated with the loss of hydrostatic pressure of the cement slurries during the initial hydration period. This also can cause we-control problems, pressure build up in the annulus between the casing strings and zonal isolation problems eventually and the remedial solutions for this are normally expensive and difficult.

The last category refers to long-term problems normally caused by poor cementing jobs. Defective drilling mud removal during the cement slurry displacement in the annulus, insufficient cement height that may lead to casing leakage and corrosion problems are some of the factors that can contribute to long-term well integrity failures and the cost to fix these problems are highly expensive.

PVI has taken into consideration these types of problems and has created two great software for these situations: CEMLab and CEMPRO+.

CEMLab - Cement Lab Data Management Software

CEMLab - Cement Lab Data Management Software

This integrated database management application formulates slurries and calculates lab amounts for all ingredients such as cement, dry and liquid additives, salts and water. It also generates weigh-up sheets, stores API test results and generates lab reports. CEMLab allows quick access to all slurry formulations and testing statuses from anywhere, anytime.

CEMPRO+ : Mud Displacement Software

CEMPRO+ : Mud Displacement Software

This mud displacement program has the capability of displacement efficiency modeling. Designed for land, offshore, conventional and/or foamed operations, CEMPRO+ accounts for many factors that can affect the efficiency of a displacement job including fluid properties, pumping rates, casing standoff and complex wellbore geometry. CEMPRO+ is the must have software for cementing operations.

Before designing your next well, keep these two models in mind to help you achieve, from the designing of the slurries to the mud displacement, a successful cementing operation.

The Managing of the Mud

Drilling mud is used to assist the drilling of wellbore into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, mud is also used for much simpler wellbores. For instance, water wells. The three main categories of drilling fluids are water-based mud, oil-based mud, and synthetic mud. The main functions of the drilling mud include providing hydrostatic pressure to prevent formation fluids from entering into the borehole, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, suspending the drill cuttings while drilling is paused, and when the drilling assembly is brought in and out of the borehole. The mud that is used for a particular job is selected to avoid formation damage and to limit corrosion.

On a drilling rig, mud is pumped from the mud pits through the drill string where it comes out of the nozzles on the drill bit, cleaning and cooling the drill bit in the process. The mud then carries the crushed or cut rock (better known as cuttings) up the annulus between the drill string and the sides of the hole

The drilling fluids carry the cuttings excavated by the drill bit up to the surface. The ability to do so depends on the cutting size, shape, density, and speed of the fluid traveling up the borehole, which is also known as annular velocity. The mud viscosity is another important property, as cuttings will settle to the bottom of the well if the viscosity is too low. Fluids that have shear thinning and elevated viscosities are efficient for wellbore cleaning. High density fluids may clean the hole adequately even with lower annular velocities, but may have a negative impact if mud weight is in excess of that needed to balance the formation pressure. For this reason, mud weight is not usually increased for hole cleaning purposes.

Mud density should be limited to the minimum necessary for well control and wellbore stability. If too great, it may fracture the formation. Depending on the mud system in use, a number of additives can improve the filter cake and therefore maintain the wellbore stability.

As we can see, mud is a vital part of drilling operations. How can mud be managed in such a way to have success in these operations? This type of mud contains carefully chosen additives to control its properties. It is the responsibility of the mud engineer to ensure that any new mud that is produced and added, meets the required specifications.

In the past, mud engineers used paper forms or Excel® spreadsheets to record mud properties, product usage, and inventory every morning. With these methods, engineers encountered problems such as disorganization of numerous daily reports and difficulty in generating end-of well recaps.

MUDPRO is a mud reporting software developed by PVI that complies with API specifications for field use.

MUDPRO - Drilling Mud Reporting Software With a backbone of databases, this all-inclusive model highly improves data gathering, sharing and management. MUDPRO is designed for mud engineers at the rig sites as well as the company men in the office. A mud engineer can use it to record mud data and generate daily reports. It can also be used by company men for reviewing and managing data, making an end-of-well recap, and comparing data between multiple wells.

Knowledge Is Power

“Knowledge is power. Information is liberating. Education is the premise of progress, in every society, in every family.”

Kofi Annan (Ghanaian diplomat)

In the petroleum industry the more knowledge we gain the more progress is made. The ability to control the downhole environment while drilling has been a dream held by drilling and reservoir engineers for decades. In the past resent years, drilling engineers focused on preventing influx of formation fluid or gas, and weighted-up their mud accordingly, but as a result, drillers found themselves indeed between the rock and a hard place.

In the early 1970s a better knowledge of drilling hydraulics started being developed. Up to this point, hydrostatic pressure and formation temperature were derived by measuring static mud weight and viscosity at the surface and calculating a pressure gradient which could be extrapolated to bit depth. Formation temperature was also calculated from a gradient. Neither parameter was precisely known. In addition, every time the mud pumps were stopped to make a connection a pressure surge was initiated when the pumps were re-started. In a formation with a tight drilling margin, this pressure spike could break down a weak spot and cause loss of circulation. Contrarily, when the drill pipe was pulled to make a bit trip or even a short trip, care had to be taken not to swab-in the well.

Drilling decisions focused on extending bit life to the maximum rather than maximizing ROP. This was accomplished by using less-aggressive bits to mitigate vibration which is the leading cause of bit wear. Float valves were installed just above the drill bit to prevent the loss of drilling fluid and to force the seawater mixture and cuttings coming down the annulus to enter the fractures. Thanks to the knowledge acquire through the years new technology has risen. Cutting-edge techniques, sustained by innovative technology, are increasing the industry's ability to safely and efficiently drill unstable formations in deepwater.

The ability to measure precisely and monitor continuously the equivalent circulating density of drilling fluid at the bit is essential for success. This is one of the functions of HYDPRO, PVI’s drilling hydraulics model.

HYDPRO - Drilling Hydraulics SoftwareThis software’s ability has allowed major strides in drilling technology that have affected safety, cost effectiveness, and efficiency. Many of the previous problems can be traced by more accurate estimations of dynamic downhole conditions.

Other functions of HYDPRO include:

  • Surge and Swab
  • Bit Optimization
  • Hole Cleaning
  • Volumetric Displacements

Like most critical undertakings, prior planning is a given. Even modular systems that are relatively easy to implement on a standard drilling unit must be carefully sized and can benefit from as much prior reservoir knowledge as possible. The benefits are important and well worth the planning effort.

A New Drilling Engineering Toolbox App

Every drilling engineer and technician knows that performing drilling engineering calculations can be a tedious and time-consuming process, considering the many researches they have to do in order to find the right results. At times, even these results are not quite exact. While technology has tremendously driven the oil and gas industry forward with the creation and development of advanced software, most of the time these are meant to be used in the office and are not so simple and portable. To assist with this issue, Pegasus Vertex, Inc. has launched the new DR.DE Lite mobile app for both Android and Apple devices. This free app was developed to provide drilling engineers and technicians with a simple, useful, paperless and portable tool to make their drilling engineering calculations easier and faster.

Dr.DE_Lite_Mobile_AppThe DR.DE Lite app is equipped with 29 functions that are divided into 11 groups.

Dr.DE Lite App: 11 GroupsFrom this great selection of functions, this tool can help you save time and efforts to get the calculations you need. In the past, drilling engineers and technicians had to obtain the information from different sources and after gathering the information manually perform the calculations and that could take up to an hour; however, now it can be done in a matter of seconds and the results are precise.

In this new tool, every function comes with three main buttons: Default, Clear and Calculate. The “Default” button gives users an example of standard input data. The “Clear” button allows users to delete all input data and the “Calculate” button performs the calculations based on the data users enter. The app collects all the information the users provide and in case the wrong data is entered, it will give a message as a warning.

For example, the “Hydraulic’ group contains four sub-functions: 1. ECD, which calculates the ECD at depth. 2. Hydrostatic pressure, which calculates the hydrostatic pressure of the mud column in a deviated well. 3. Pressure drop (Bingham) annulus, which calculates the pressure drop in an annular section for Bingham plastic fluids. 4. Pressure drop (Power law) annulus, which calculates the pressure drop in an annular section for power-law fluids.

Dr.DE Lite: Pressure DropIn the “Pressure drop” function, users can specify the wellbore configuration, as well as fluid properties and flow rates. DR.DE Lite performs calculations for fluid velocity, flow pattern, pressure drop, Reynolds number and other key parameters for different flow patterns.

The DR.DE Lite app is the perfect tool that complements your work. It’s easy to download, easy to use, very convenient and free. To download DR.DE Lite, scan the QR code or download the app from your mobile play store.

Dr.DE_Lite: Free Drilling Engineering Toolbox Mobile App

Floating Egg

I did a simple science project with my 8-year-old daughter to show the action of buoyancy.

Step 1: Put a raw egg in a glass full of water. The egg sinks to the bottom.

Step 2: Keep adding salt and stir the water.  You will feel guilty of wasting too much salt, but eventually, the egg arises.

Before / After Adding Salt

My daughter and I were both amazed by this simple demonstration of buoyancy of salt water. Recall that Archimedes’ principle states that the upward force on a submerged object (egg) is equal to the weight of the water that it displaces. Salt water weights more than fresh water, this difference of upward force (buoyancy) makes the egg arise.

In drilling mud situations, saltwater drilling fluids can be formulated with high-density brines, such as calcium chloride, calcium bromide, etc. The mud weight is dependent upon the specific gravity (SG) of salts added and concentration of these salts. The heavier the mud, the higher the bottom hole pressure is. Note that one of the main functions of drilling fluids is to provide hydrostatic pressure to prevent formation fluids from entering into the well. Heavy mud brings some advantages and some disadvantages to other aspects of drilling operations because of the buoyancy it creates.

Buoyancy makes drill string appear light. This reduces the side force, which pushes drill string against wellbore. Therefore, there is less torque and drag for a heavier drilling fluid system, but what helps also causes problems in this case: too much buoyancy revokes the effectiveness of transferring the pipe weight to the bit.

When cementing a casing, due to the large size of the casing and the big difference of fluid densities in the annulus and inside the pipe, the buoyancy could be so great that the casing could be pushed out of the hole if it is not chained down.

Let’s use Dr.DE (drilling engineering tool box software) to show a couple of examples.

Consider an 11.75” OD casing with weight of 47lb/ft. The casing shoe is at 12,345 ft in a vertical well. The annulus is full of cement slurry of 16ppg. We assume mud weight of 8.33 ppg. With the help of Dr.DE the calculation shows that the casing will be lifted up.

Casing will be lifited up | Dr.DE - drilling toolbox

Casing Will Be Lifited Up

Now, change the mud weight to 9 ppg, due to this change, the hydraulic pressure inside the casing increases and the casing will not be lifted up by the buoyancy.

Casing will NOT be lifited up | Dr. DE Drilling Toolbox

Casing will NOT be lifited up