API RP 65-1:2018 pdf free download.Cementing Shallow-water Flow Zones in Deepwater Wells
4 Drilling Practices to Reduce the Risk of Shallow-water Flows
4.1 General Tophole drilling practices have a significant impact on the ability to achieve zonal isolation in the presence of shallow-water flows. The importance of constructing a structurally sound foundation for the well cannot be overemphasized. Failure to establish and maintain zonal isolation in the tophole section of a deepwater well will, in many cases, compromise the ability to achieve the overall well objectives. Poor drilling practices can lead to issues ranging from lower-than-expected leak-off values at the casing shoe that impact the ability to maintain the planned casing program, to the loss of containment of wellbore fluids. From a planning and job execution perspective, it is imperative that information about the conditions expected during the drilling of the tophole interval be communicated to all parties involved in the cementing operations.
A summary of the results from the hazard assessment of the drill site should be provided to the cementing service provider to be used in the development of the cementing program, or be used by the operator in the development of the cementing basis of design. Typically, the information provided in the shallow hazard assessment will include the expected location, thickness, and severity of shallow-water flow intervals, as well as other hazards, such as possible hydrocarbon bearing or loss circulation zones. Representatives from the cementing service provider and operator should review the mitigation measures being proposed for the anticipated tophole hazards.
4.2 Well Spacing Individual well spacing and drilling order during deepwater development should be designed to minimize the impact of drilling operations on adjacent wells. Shallow-water flow can cause changes in the local mechanical stresses affecting both the well experiencing the flow and adjacent wells. Well arrangement with the greatest distance between adjacent wellbores (at the flow zone) can reduce the risk of damage to a well from a nearby well that is experiencing flow. In cases where deepwater development includes wells currently being produced intermixed with wells that are being drilled, be aware of the temperature influence a producing well may have on an adjacent wellbore that is being drilled.
4.3 Hole Conditions The condition of the borehole established during the drilling operation will have a major bearing on the quality of the hydraulic isolation established by the cementing operation. Of the hole conditions impacting cementing success, hole diameter, hole tortuosity, and wellbore stability are of engineering concern.
4.4 Hole Enlargement Hole enlargement makes it difficult to successfully install and cement a casing string, which can lead to post-cementing problems such as casing buckling. Buckled casing in the enlarged sections may prevent re-entry into the well. Uncontrolled flows can also lead to compaction and subsidence of the flow zones, impacting the integrity of nearby wells or structures. Hole enlargement can lead to lower annular velocities, increasing the likelihood of cuttings loading while drilling, raising ECD, and potentially causing annular pack-off. Lower annular velocities also make it more difficult to displace wellbore fluids during cementing. Hole enlargement makes centralization (an important element of effective drilling fluid removal) more difficult.
Causes of hole enlargement include:
— removal or “mining” of formation materials from the wellbore by shallow-water flows;
— hydraulic erosion, which is caused by excessive bit nozzle velocity and turbulence at the bit;
— a high fluid loss drilling fluid causing high near-wellbore pore pressures (no distinct pressure gradient across a sealing filter cake).
NOTE This means that near-wellbore pore pressure is equal to the pressure exerted by the drilling fluid, resulting in a near-wellbore radial effective stress of zero.
This loss of stress eliminates the effective overbalance acting to support the formation. Hole enlargement is controlled in a variety of ways, including optimizing the drilling parameters and the density and composition of the drilling fluid.API RP 65-1 pdf download.API RP 65-1:2018 pdf free download
