The decline in oil prices has been particularly difficult for shale plays because of the challenging economics. Although unconventional formations are the latest frontier in oil and gas development, shale plays are associated with long and complex laterals; high-angle well sections; dense, low-permeability rock; and harsh downhole conditions, all of which increase operational costs and shrink profit margins.

Now more than ever operators are seeking strategies to spend less money by reducing rig time, eliminating nonproductive time (NPT) and mitigating equipment damage.

When drilling in shale plays, conventional mud motors often fail to deliver the high accuracy and reliability required to navigate sweet spots efficiently and maximize reservoir contact. To improve economics, drilling tools must go faster and farther, in fewer trips and with more precise and nimble geosteering. As a result of new technologies, the drilling process is rife with opportunities for lowering costs while helping to enhance ultimate recovery.

Economic challenges in Eagle Ford

Located in South Texas, the Eagle Ford shale play is the largest oil and gas development in the world based on capital investment. It is also home to the largest oil field in the U.S., the Eagleville, which produced nearly 240 MMbbl in 2013. The breakeven thresholds for shale projects in the Eagle Ford are among the lowest in the U.S., but at $50/bbl, even these margins are thin.

Deeper, faster, single-trip drilling

Although rotary steerable systems (RSS) typically cost twice as much per day as conventional mud motors, the savings in rig time and the improved borehole quality offset this investment many times over. The Weatherford Revolution RSS (Figure 1) decreases drilling costs by maximizing efficiency and ROP.

FIGURE 1. The Weatherford Revolution RSS incorporates point-the-bit technology for improved geosteering along the planned well path and enables deeper, faster drilling with precision well placement—often in a single run. (Source: Weatherford)

Using point-the-bit technology for improved geosteering along the planned well path, the RSS enables drilling to greater depths, at faster rates, in fewer trips and with precise wellbore placement—all while leaving a smooth, clean borehole for completion.

The Revolution RSS encompasses a suite of application-specific drilling technologies that deliver high build rates—a maximum of 16°/30 m (16°/100 ft)—and maintain stability at any inclination, which makes it well suited for drilling vertical, deviated, horizontal and extended-reach sections in one run. This RSS can also withstand bottomhole temperatures up to 175 C (347 F) and bottomhole pressures up to 25,000 psi.

At the Weatherford Technology Center in Tewkesbury, England, technicians tested the Revolution RSS under various simulated environmental conditions—ranging from backward whirl and severe torsional vibration to high temperatures and pressures—to assure reliable performance in the most extreme conditions.

Hostile-environment logging

When combined with the hostile-environment-logging (HEL) MWD system, the Revolution RSS offers an integrated approach to drilling. The HEL MWD system incorporates sensors that monitor the wellbore environment and capture a full range of data in real time.

Armed with this information, operators can make adjustments while drilling, which reduce the risks of damaging equipment, incurring NPT and prolonging the drilling process.

Advanced vibration detection

The hard carbonate rock overlying the Eagle Ford Shale causes excessive vibration that accelerates wear on the drillbit and damages drilling tools. This type of vibration cannot be detected from surface-based measurements and occurs at frequencies outside the measurement range for conventional drilling sensors.

Placing advanced vibration sensors downhole is critical in preventing bit wear and tool damage. By incorporating technologies such as the Weatherford Total Vibration Monitor (TVM) on drilling tools, operators have identified high-frequency torsional oscillation (HFTO) in the bottomhole assembly (BHA) as the culprit for vibration and bit wear (Figure 2).

FIGURE 2. The graph shows HFTO with bit speeds fluctuating at 150 rpm, 60 times per second. Severe torsional vibration in excess of 40g causes rapid fluctuations in bit speed and can cause the bit to instantaneously travel backward against the rock face. (Source: Weatherford)

HFTO is the result of BHA torsional resonances, which are prompted by distinct rock-cutting processes that occur when drilling hard formations. In addition to fatigue damage to drilling tools, HFTO also causes rapid fluctuations in the bit speed, which can lead to the instantaneous backward rotation of the bit against the formation. This dulls drillbits very quickly.

Detecting and mitigating HFTO and other adverse drilling dynamics in hard carbonate rocks is the key to drilling longer laterals through shale. The TVM can be integrated into the Revolution RSS and any other Weatherford MWD/LWD tool for enhanced control over shock and vibration.

Real-time optimization

Bit wear and drilling tool damage are avoided by combining vibration sensors such as the TVM with real-time monitoring. Incorporating Weatherford software and technical support at regional real-time operations centers (RTOCs) helps to ensure that downhole data are constantly monitored and any issues are addressed immediately.

Additionally, subject-matter experts at RTOCs recommend and implement best drilling practices in close collaboration with operators. As a result, drilling systems remain in optimal condition longer, and operators can drill long laterals through challenging geology to total depth.

Case studies

The Revolution RSS routinely drills more than 4,572 m (15,000 ft) measured depth (MD) in a single run. Recently in the Eagle Ford it set a global company record for run length by drilling 4,774 m (15,662 ft) in a single run.

In one Eagle Ford project, the RSS drilled wells in half the time the operator expected based on the average time it took previously to drill the fastest 10% of wells. The client was able to drill all planned 49 wells to an average MD of 5,791 m (19,000 ft) using only half the number of rotary rigs originally anticipated.

Especially when combined with advanced vibration sensors, real-time data-gathering capabilities, and monitoring software and support, the Revolution RSS is enabling more complex unconventional wells to be drilled worldwide. Compared to conventional motors, the Revolution RSS improves field economics by drilling more efficiently, extending well reach, improving bit life, reducing rig count and creating a smooth borehole.

The technology has the added benefit of precise navigation—and real-time adjusting of operational parameters—for avoiding problem zones, mitigating equipment damage and maximizing reservoir contact.

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