11分鐘！DeepFX-L炫技神速固井

In the surface interval of offshore wells, shallow-water flows from overpressured shallow sediments can be a challenge during casing and cementing operations. In deepwater, this challenge can be exacerbated because of the proximity of the overpressurized zones to the mudline, the relative water depth and deepwater drilling techniques. “When we go to cement across the section, we have to design a slurry that can keep the shallow-water flow in place and not let it penetrate or flow,” Simon Turton, Halliburton’s Strategic Business Manager for Cementing, said.

To combat the shallow-water flows, Halliburton has developed Deep FX-L, a liquid cement additive that enables the cement to reach critical gel strength in an average of 11 minutes and stem the shallow-water flows. It allows gel strength to build by virtue of the calcium-silicate-hydrate setting. Without the additive, Halliburton says, this would take hours. Critical gel strength is defined as 500 lb/sq ft.

“It’s assumed that when a slurry reaches that number, then it is impenetrable by gas, oil, water or by any other substance that might flow,” Mr Turton said. The additive has no known slurry limitations and can be used in both heavy and lightweight cements, according to the company.The Deep FX-L additive has undergone field trials in the deepwater Gulf of Mexico, and Halliburton is currently commercializing this product.

The company is also developing additives to address challenges that occur further downhole. “We quite often find that the deeper we go, the lighter cement that we may need to use,” Mr Turton said. Lightweight cements with densities under 15.8 ppg are often used to achieve the lower ECD required to stay within the narrow pore pressure and fracture gradients common in deepwater wells.

There are a few ways to make a lightweight cement. The first is to add more water to the cement, but this can compromise the final properties of the cement, Mr Turton said. Adding a gaseous phase – using nitrogen, for example – can make a lightweight foam cement. However, there is often not enough space on the rig floor to accommodate the equipment required to add gas to cement. Such equipment includes tanks and potentially a nitrogen converter. The final option for creating a lightweight cement is to use a lightweight particulate additive.Offshore and deepwater cementing must overcome unique challenges including logistics, shallow water flow and gas migration. DeepFXTM-L additive is designed to enable logistics efficiencies and to be blended with cementing systems to help address both shallow water flow and gas migration conditions.

Fluid Loss and Gas Migration

Gas migration can occur when the slurry is static after pumping stops. Loss of fluid from the slurry to the formation can reduce the hydrostatic pressure in the column and provide the opportunity for gas or fluids to migrate into the slurry. This migration can progress until the cement column achieves a gel strength sufficient to resist the pressure exerted from the formation. The progression of formation gas/fluid migration can leave flow channels through the cement sheath. Depending on formation pressure and the hydrostatic pressure from the column of fluid, gas or fluid migration typically begins when the cement reaches a gel strength of approximately 100 lbf/100 ft2 and can then resist the influx
once it has achieved a gel strength of 500 lbf/100 ft2. DeepFX-L additive helps control fluid loss from the slurry system for greater stability. Additionally, it enables early gel strength, expediting the time for the slurry to achieve 500 lbf/100 ft2 once pumping has stopped. Because it is a liquid additive, it does not require bulk blending, but instead can be mixed into the slurry on the rig during cementing operations.

Shallow Water Flow

Shallow water flow is a result of seawater or gas getting trapped due to rapidly depositing sands across an expanse of young formations. Then, as newer formation layers are added, pressure on the sand builds due to the weight of the overburden. Drilling through these zones releases the pressure and can result in wash outs of the younger, unconsolidated formation layers. These washouts can be so significant that the wellhead is lost. When cementing conductor or surface casing across these zones, the hydrostatic weight of the column of cement is designed to accommodate what is typically a weak or unconsolidated (young) formation, yet transmit hydrostatic pressure to the formation with sufficient force to help keep the water in situ. Thus, a lightweight cement system with a short transition time is typically used. DeepFX-L additive helps shorten transition time for lightweight cement systems without impacting foam stability and without impacting mechanical properties.

Benefits

• A single additive addresses two challenges: providing fluid-loss control in slurries mixed with salt and/or seawater; and shortens transition times from slurry to solid;
• helping minimize the gel phase of the cement;
• Can be used in foamed slurries without impacting foam stability or mechanical properties;
• Liquid additive that does not require bulk blending.

Halliburton is preparing to launch a new lightweight particulate additive, Liquilite, later this year. It consists of hollow glass spheres suspended in a liquid phase and is added to the cement as it is going downhole. Existing light- weight cements use hollow glass spheres blended in with dry cement before being mixed and pumped downhole. This creates an opportunity for the glass spheres to be crushed while blending the cement and transferring the dry cement, especially as pressure is used for both of these two processes. Service companies then have to use additional spheres to compensate for glass spheres lost to crushing. With Liquilite, this crushing effect is avoided, allowing Halliburton to do away with extra glass spheres and, in turn, reducing the cost of the additive.

Both the Liquilite and Deep FX-L additives are added as the cement is pumped downhole, not pre-blended with the cement. This allows the operator to increase or reduce the amount of additive used on the fly, if needed. “If they don’t use it on the job, there’s no waste cost or disposal associated,” Mr Turton said. “It’s just the neat cement that’s left in the tanks and it can be topped off and then used on the next hole section.”

Case History

CHALLENGE-Gulf of Mexico

• The field presented with a minor shallow water flow(SWF) hazard;
• Previous cement design solutions require multiple liquid additives to address SWF, increasing the already logistical challenges of riserless cementing;
• Overcome the unique deepwater challenges including logistics, SWF, and gas migration.

SOLUTION – DeepFX?-L additive

• Single additive addressing both SWF and gas migration conditions;
• Enabled logistics efficiencies by minimizing the number of liquid additives;
• Allowed for the cement slurry design to meet API 65 Part 1 specifications.

RESULT

• Provided fluid-loss control in slurries mixed wit;
• Shortened transition times from slurry to solid, helping minimize the gel phase of the cement;
• Can be used in foamed slurries without impacting foam stability or mechanical properties.