Saving Expensive Offshore Deepwater Rig Time by Modeling Accurate Subsea/Subsea-Floor Temperature Modeling for Cementing Operations

Abstract

Accurate temperature modeling on an offshore deepwater well or potentially any other type of well can result in reduced, non-productive time (NPT) attributed to waiting on cement (WOC) time. Understanding the downhole temperature behavior and heat recovery during the static time after placement of cement slurry can provide an opportunity to minimize WOC-time for compressive-strength development. Drilling engineers encounter a variety of requirements by regulatory agencies across the globe concerning cementing operations. Although the regulatory-agency guidelines and expectations in many cases are detailed and challenging, the operational requirement and cost-saving prospects by operators go beyond some of these recommended/required expectations. Almost any optimization that can expedite commencement of the drilling operation after a cement job (for example, drilling, completing, moving rig) should improve the cost-effectiveness of the drilling program. Water temperature gradient profiles from sea surface to seabed through shallow formations below the seabed exhibit diverse characteristics in different fields. An accurate bottomhole static temperature (BHST), or the undisturbed bottomhole temperature (BHT) and understanding the bottomhole circulating temperature (BHCT) behavior is a crucial factor to success of deepwater field developments. This paper will discuss how best practices in combination with optimized downhole temperature modeling can potentially reduce the number of hours in WOC-time without introducing any additional risk factors into the cementing/drilling operations. Calculating accurate downhole temperature and pressure profiles, which are also used for pipe-body movement and casing-and tubing-load analysis, assists cementing, drilling, and completion engineers to produce highly effective solutions. Introduction As the oil and gas industry witnesses less conventionally accessible hydrocarbon reservoirs, the focus shifts more towards large reservoirs in more challenging environments. These resources have become more technically and economically accessible as new technologies emerge to make more effective exploration possible. One of the most promising areas of discovery is the deep/ultra deepwater offshore reservoirs. In many cases, deepwater reservoirs, such as the North Sea have shown more productivity and relatively lower life compared to average deep wells on land. Many wells have also been drilled in shallower waters where drilling operations are commonly less complex to conduct. Deep and ultra deepwater reservoirs have historically been less explored (compared to shallow-water fields) in spite of their great potential because of the complexity and availability of the required technologies, including cementing. Today's cementing technologies allow the engineers to plan ahead and design sealant systems that will endure or exceed all the operational cyclical conditions. Zonal isolation effectiveness and casing protection are two of the critical factors in every well's life that will help ensure production continuity and minimal to zero remedial costs. Some deepwater wells in the GOM are known to produce more than 13,000 BOPD (barrels of oil per day). In the Middle East, many wells produce in excess of 15,000 to 20,000 BOPD. It is more beneficial to seek and explore some of the deeperwater opportunities, as these reservoirs can be very rewarding if wells are drilled and completed successfully. Additionally, a general industry rule for offshore-well classification in regards to water depths is to define shallow as depths of less than 1,500 ft (457 m) of water, deep as 1,500–4,000 ft (457–1219 m) of water, and ultra-deepwater as 4,000 ft (1219 m) of water and greater. Recently, some operators have been calling anything that exceeds the 5,000 ft (1524 m) of water depth "deep water" because drilling in 1,500 ft (457 m) of water has become rudimentary as a result of achieved technological advancement and experience.

SS: Deepwater Cementing: Key Factors to Consider for Sidetrack Plug Success in Deepwater Cementing Operations Using Synthetic Based Muds

“…7,8, 9 Besides the traditional wireline measurement, drilling and evaluation instruments such as MWD/LWD downhole gauges will provide some useful temperature data to ballpark the cementing BHCT for the cement lab testing. Special consideration to the effects of ambient surface conditions at the time of the job, water temperature gradient and seafloor temperature, and the given geothermal undisturbed formation temperature gradient from seafloor to planned true vertical depth for determination of correct cementing temperatures.…”