Low invasion well construction fluids

Reducing whole mud and filtrate invasion to as low a level as possible during drilling will minimise and often eliminate problems such as induced loss circulation, wellbore instability and differential sticking. Very low invasion also generally means less formation damage and so higher well productivity. The same low invasion concept can be applied to cement spacers to prevent losses during cementing.

“There is an alternative approach to using bridging agents such as calcium carbonate: use soft particles that can deform into pores and fractures to form a thin, ultra-low permeability barrier that protects the formations exposed to the drilling fluid.”
-Impact Fluid Solutions

Low Invasion Muds

There are many ways to reduce whole mud and filtrate invasion when drilling. These often involve careful sizing of particles in the mud system to match a model particle size distribution that optimises bridging of pore throats or small fractures. The particles are usually hard materials such as calcium carbonate. Sometimes - for example if the requirement is to seal fractures, or engineer a wellbore strengthening effect through the stress cage technique - substantial quantities of large particles are needed. This sized particle approach to minimising invasion brings several challenges:  

• We need to know the size of the pore throats or fractures we are trying to protect.
• We need to add 20lb/bbl, 30lb/bbl or more of the sized solid.
• Brittle solids such as calcium carbonate are ground during drilling, so the optimum size distribution for sealing is quickly lost.
• If coarse solids are used, the solids control system must be bypassed or we must accept that the particles will be screened out at the shale shakers.

There is an alternative approach to using bridging agents such as calcium carbonate: use soft particles that can deform into pores and fractures to form a thin, ultra-low permeability barrier that protects the formations exposed to the drilling fluid. Take, for example, Impact's additive FLC2000: This product is designed to form soft aggregates in water-based, oil-based and synthetic-based muds. It is environmentally acceptable, stable at temperatures in excess of 200^oC (400^oF) and is effective at only 4-6lb/bbl in most mud systems. This one product has been demonstrated to seal matrix permeabilities from less than a milliDarcy to over 100 Darcies - so it offers far more flexibility in terms of what size pores can be protected than can a single particle size distribution of calcium carbonate and there is no need to change the blend of FLC2000 as we move from one formation type to another. FLC2000 also seals fractures up to approximately 250 microns wide where it will maintain a seal even with overbalances in excess of 1600psi. In addition, the product gives wellbore strengthening, not by the stress cage mechanism but by preventing fracture propagation because it forms a protective ultra-low permeability "membrane". The reader will, at first sight, perhaps think that the above claims are excessive for a single mud additive. However, on closer reading, they will appreciate that all the claims come from one single feature - the exceptional low levels of mud and filtrate invasion that result from the use of FLC2000.

What do the low invasion properties imparted to a mud by FLC2000 mean in practical terms? We can demonstrate benefits in the following areas:

• An excellent degree of wellbore strengthening means that higher mud weights can be run without inducing lost circulation. This is particularly beneficial when drilling depleted zones and zones with highly anisotropic downhole stresses.
• Improved well productivity, since much reduced invasion generally means less formation damage. If the completion method requires it, the thin filter cake formed by FLC2000 is easily removed from pay zones either by simply flowing the well or by the use of a specially formulated breaker system. Figure 1 compares the depth of invasion into the pay zone in wells with and without the additive.

Figure 1. Logs from the sandstone reservoir section of Colombian wells drilled with water based muds. The left hand image shows resistivity data in the sand drilled without the FLC2000 additive. The different resistivity values at different depths inside the formation indicate deep invasion: approximately 1 metre. The right hand image shows the same formation drilled with the FLC2000 system: here all but the shallowest reading rate traces are largely superimposed, indicating much less invasion. The logging company estimated only 10 cm invasion with the FLC2000.

• FLC2000 will protect brittle shales and coals that will otherwise become fractured. When mud invades these fractures, severe hole instability can result. Sealing the fractures will prevent cavings and give much better hole condition. Figure 2 compares the calliper from wells drilled in brittle shales with and without the additive.
• The thin filter cake produced by FLC2000 will greatly reduce the risk of differential pressure sticking.

Figure 2. Logs from a shale section of Colombian wells drilled with water based muds. The left hand image shows severe hole enlargement in the shale drilled without the FLC2000 additive. In comparison, the right hand image shows the near-gauge hole obtained in the same formation drilled with the FLC2000 system.

Follow the links to our website to access technical details and extensive case histories. Impact's low invasion additives have been used extensively in many mud types and in many regions of the world.

Low Invasion Cementing Spacers

We can take the concept of low invasion drilling muds and adapt the FLC2000 technology to produce cementing spacers. These spacers give an excellent degree of wellbore strengthening ahead of cement, meaning that loss of cement to the formation is minimised and often eliminated. The result is a much better cement job with excellent CBLs (Figure 3), cement tops at the planned depth and superior zonal isolation. Our low invasion spacer is compatible with all other common spacers and spacer components and with all mud types.

Figure 3. Cement Bond Logs for wells cemented with conventional spacers and the low invasion spacer.

Follow the links to our website to access technical details and extensive case histories.

Impact's Commitment to Customer Service, Value and the Environment

Impact understands that our products must give value to the customer and must be properly supported. We have extensive laboratory facilities to provide technical support and encourage our clients to work closely with us, sharing data and working as a team so that we can ensure our products bring the maximum benefit.

We are proud to offer products that conform to current and anticipated environmental requirements. Our products are not harmful to animal life or plants. They are readily biodegradable and do not bioaccumulate.