Comparative analysis of horizontal drilling techniques: performance and applicability assessment

Horizontal drilling encompasses a spectrum of approaches that enable wellbores to deviate significantly from vertical trajectories, generally adopting a latitudinal orientation at depth. In contrast, conventional drilling techniques, such as vertical and directional systems, are limited in the achievable angle between the wellbore and horizontal plane. More precisely, these definitions apply to the inclination of a rigid segment of the wellbore – commonly termed the build-up section where inclination deviates intentionally from a vertical direction to reach a horizontal azimuth. Although horizontal drilling has been undertaken for several decades, recent innovations in rotary steerable systems (RSS), measurement-while-drilling (MWD) and logging-while-drilling (LWD) technologies, and associated investigations into specific drilling techniques have heightened industry interest. The assessment framework outlined here seeks to evaluate horizontal drilling techniques on the basis of both performance and applicability, taking into account multiple datasets drawn from well-known fields. The vertical build-up section is generally a prerequisite for both directional drilling (DD) and horizontal approaches. In this context, the rotary steerable system (RSS) constitutes a significant advance in capability within directional drilling (DD) applications. Consequently, although DD-RSS techniques share a similar wellbore geometry at a given point in time, the analytical comparison focuses on three approaches that uniquely or in combination achieve the horizontal trajectory within the rotary drilling mode: mechanical paradox/step-rate, reservoir-driven steering, and geopositioning techniques.

Given the advent of innovative downhole sensors integrated with advanced telemetry and control systems, a variety of horizontal drilling techniques have been developed to facilitate accurate steering, maintain wellbore integrity, and mitigate formation and bit-related problems. These techniques leverage information from surface and downhole measurements to adapt both trajectory and operational parameters in real time, thus enabling performance enhancement in complex geological settings.

Directional drilling with rotary steerable systems (RSSs) has gained widespread adoption on a global scale. The technology permits continuous drilling along planned trajectories and provides drilling organizations with a powerful tool for wellbore placement. RSS is particularly compatible with measurement-while-drilling (MWD) and logging-while-drilling (LWD) technologies, as it allows wells to be drilled to required targets without sidetracking or re-entry due to inadequate bottomhole position knowledge 

The mechanical paradox and step-rate techniques constitute two emerging approaches that capitalise on the oil-rock-liquid interaction between downhole pressure and the influx rate of an aquifer. Theoretical research confirms the feasibility of mechanical-paradox-shaped-frac-pressure – local-envelop-solution-based wellbore position estimation and demonstrates the capability of step-rate analysis to determine both water – hydrocarbon contact position and initial water ratio with satisfactory accuracy.

The integration of measurement-while-drilling (MWD) and logging-while-drilling (LWD) technologies remains a pivotal advancement within rotary-drilling systems. In conventional approaches, critical measurements of hydrocarbon reservoirs and lithology encountered along the wellbore are captured at specified time intervals, generally requiring several physical trips to the surface. 

Consequently, decisions affecting the drilling programme are taken independently from the drilling process. Conversely, simultaneous acquisition and transmission of measurements remains operational during the drilling phase. Specific features such as formation resistivity, pressure, temperature, density, and acoustic-wave velocities are continuously relayed from downhole to surface in practically real-time. An MWD system capable of transmitting a comprehensive range of measurements alters both the data-acquisition strategy and the decision-making cadence.

The methodology for comparative analysis establishes an extensive rationale covering measurement, drilling, geology, and regulatory considerations across different drilling applications. Defined parameters primarily address penetration rate, drilling efficiency, and time to target as critical performance metrics. A detailed overview of dimensional and process metrics supplement these measurements, all of which undertake normalization subsequent to individual data analyses. Uncertainty surrounding prevalent parameters and a dedicated focus on dual-branch lateral drilling principally guide exposition of MWD and MWD technologies.

Borehole quality remains a vital performance indicator, serving as a surrogate for potential completion hazards and future intervention costs. The nature of conventional rotary drilling encompasses continuous removal of drilled materials, with the associated capacities, logistics, and challenges widely acknowledged among practitioners. In drilling poor-drainage reservoirs, the presence of cuttings and substantial amounts of mud represents a concern. Key contributors to hole-cleaning effectiveness encompass the mud system, flow-rate management, and any co-polymers employed; these factors require independent characterization alongside the primary set of parameters. Impediments to cuttings removal, particularly with expansive cuttings loads or through permeable formations, are well documented.

Some historical applications of rotary steerable systems (RSS) describe capacity to maintain trajectory to a specified target. Descriptions of trajectory control strategies encompass two principal alternatives: active and reactive. In active schemes, the desired curve or template is specified downhole, whereas, in a reactive regime, the objectives rely on the position of the bottom-hole assembly (BHA) in relation to pre-defined limits, together with adjustments to the wellhead angle. Experience highlights reactive schemes as broadly dominant within the current market.

The efficiency and effectiveness of the analysed techniques correlate with the geological context, particularly the complexity of the lithology and the presence of pre-existing fractures. Lateral-holes drilling is preferred when fracture density is low, allowing the simultaneous drainage of multiple unconventional reservoirs, as in the 12,000 ft reach achieved in Wyoming’s Niobrara shale 

When the lithological succession becomes more complex, rotary steerable systems prove advantageous. Their use results in a 40% reduction in the overall drilling time spanning multiple unconventional reservoirs with a lateral density of four 

On the other hand, managed-pressure drilling with open-hole completions becomes necessary when pre-existing fractures complicate the manoeuvring of the conventional wellbore. To widen the fracture system and cover a more extensive drainage area, a total coverage of 7,500 ft is reached, enabling the drainage of four unconventional reservoirs 

Finally, steerable slip-resistant assemblies facilitate the deployment of lateral sections in schematised architectures such as lenticular and sinuous accumulation geometries in offshore regions where drilling tendons exert a high axial force.

Onshore shale plays Lateral drilling techniques applicable include dual-branch systems, rotary steerable systems, and managed pressure drilling with open hole completions. The first two options face limitations as reservoir depth increases beyond ~3000 m, while rotary steerable systems are also feasible at depths much greater than 3000 m, although hole cleaning issues must be anticipated.

Offshore reservoirs the same techniques as those indicated for onshore shale plays are also employed offshore. Dual-branch systems, however, are rarely if ever deployed under such conditions. Lateral drilling in offshore settings is often governed more by well safety regulations than specific geological parameters. Thin-skinned and faulted regions – Lateral drilling techniques applicable in these contexts encompass dual-branch systems, managed pressure drilling with open hole completions, and steerable slip-resistant assemblies. These techniques remain suitable regardless of lithology or fracture density. For shore condition, however, dual-branch systems are restricted by the common reliance on over/under balancing 

High-pressure, high-temperature environments Applicable techniques include dual-branch systems, rotary steerable systems, and managed pressure drilling with open hole completions. Operational constraints determine whether dual-branch or rotary steerable systems are favoured during a given phase.

Two techniques stand out: managed pressure drilling and rotary steerable systems. The first enables either dual-branch or single-entry laterals to be drilled, while the second potentially allows a wide variety of lateral configurations to be deployed. Nevertheless, because dual-branch techniques are limited to relatively shallow formations, the recommended options must be narrowed further. In such circumstances, and given the continued and pervasive deployment of the alternative across numerous regions, rotary steerable systems emerge as the preferred choice.

Characterization of carbonate reservoirs often remains hindered by diverse diagenetic processes that yield wide-ranging property variations throughout the covering rock The concept of reservoir heterogeneity defined as the variation of rock properties as a function of location represents a critical factor in modeling and prediction of reservoir behavior. Because the majority of formations exhibit some degree of heterogeneity, with spatial variation in mineralogy, organic content, and natural fractures, accurate treatment of the associated features is essential for formulation of efficient investment strategies. Techniques such as the Dykstra-Parsons method for permeability variations and the Lorenz coefficient for a lumped-statistics measure provide insight into vertical heterogeneity of the core material. Despite adherence to the homogeneity assumption in many investigations, substantial deviations are frequently observed; hence a meticulous approach to the multi-layer interpretations remains imperative for subsequent acquisitions. Rock properties, including permeability, porosity, wettability, and water saturation, can be classified into units possessing similar characteristics as a means of honing the understanding of flow.