Software programs aid horizontal drilling decisions

William C. Maurer
Maurer Engineering

Complexity requires more detailed planning to lessen cost and risk

Horizontal drilling and completion presents a challenging array of downhole problems. [25051 bytes]
Borehole stability model (BSTAB) tracks tension, shear, and collapse, using mud weight and inclination angle inputs.[27490 bytes]
Wellbore hydraulics model (HYMOD) helps plan drilling fluid programs and remain within safe fracture pressure boundaries.[34715 bytes]
This tubular buckling model (BUCKLE) calculates buckling loads for drill pipe and casing and predicts drag load increase caused by buckling.[28750 bytes]

Horizontal drilling is much more complex than vertical drilling. Most of the problems encountered when drilling vertical wells are compounded when drilling vertical wells. The use of computers is therefore critical to successfully plan, drill, and complete horizontal wells.

The use of state-of-the-art software greatly increases the efficiency of engineers and allows them to:

Select the best candidate reservoirs for horizontal drilling
Optimize well placement in candidate reservoirs
More accurately calculate drilling parameters
Optimize drilling, completion, and workover operations
Identify and avoid potential field problems
Troubleshoot field problems before they become critical.

Good software can increase the efficiency and output of drilling engineers 50-100% by allowing them to more thoroughly analyze and understand problems and to evaluate hundreds of cases per day. Engineers equipped with good software can significantly reduce the cost and risk of horizontal wells by optimizing drilling operations and minimizing field problems.

A major part of Maurer Engineering's joint industry DEA 44 Horizontal Well Technology project funded by 120 companies from 22 countries involves developing software needed by participants to plan horizontal wells and to anticipate and overcome field problems. The 25 DEA programs apply equally well to vertical, inclined, and horizontal wells.

During horizontal well operations, the DEA programs are used in sequence, starting with the reservoir programs, followed by the drilling, completion, and workover programs. In addition to well planning, these program are used to troubleshoot problems during field drilling and completion operations.

Reservoir screening

RESMOD is used to predict oil and gas production rates from vertical and horizontal wells (unfractured, naturally fractured, and hydraulically fractured) and to optimize the location and shape of the horizontal wells. RMATCH allows reservoir engineers to quickly history-match vertical and horizontal wells to provide input data for RESMOD.

HOTWELL, written by Dr. Roger Butler of the University of Calgary, calculates steam requirements, temperature distributions, and production rates for heavy oil reservoirs produced by gravity-assisted steam flooding operations.

PROMOD is a multi-phase well flow model used to optimize completions in two-phase flow horizontal wells, and for designing and optimizing gas lift and velocity string designs. HOPE, written by Dr. Omar Kelkan of the University of Tulsa, is a two-phase flow model used to optimize the design of surface lines, surface chokes, safety valves, and tubing in two-phase horizontal wells.

Drilling models

WELPATH allows engineers to design and optimize complex 2D and 3D horizontal well profiles and to optimize their trajectories in reservoirs. The program contains many advanced features, including a wellbore collision program, lease boundary alarms, 3D rotation, and survey files for use in the other DEA programs.

HYDMOD is a wellbore hydraulics model used to plan hydraulics programs, to analyze cuttings lifting rates, to ensure staying within pore pressure and fracture pressure limits, and to optimize drilling parameters.

BSTAB is a borehole stability model used to ensure that mud weights remain within collapse and fracture limits, to ensure wellbore integrity at higher angles where the equivalent circulating density (ECD) becomes more critical.

BSTRESS calculates stresses in the rock surrounding the wellbore for more detailed borehole stability studies.

DDRAG is used to calculate torque and drag loads on drillstrings during drilling and completion operations. The program identifies abnormal torque and drag conditions that indicate hole problems, thus allowing drillers to take remedial actions before these problems reach a critical stage. DDRAG is the most widely used PC program in the drilling industry and is used by hundreds of engineers daily around the world to overcome serious torque and drag problems encountered while drilling and completing horizontal or long-reach wells.

BUCKLE calculates buckling loads for drill pipe and casing, and predicts the increase in drag load caused by buckling. Buckling lockup is a major problem in extended reach and long horizontal wells, often limiting the length of these wells.

DPLlFE predicts drill-string fatigue life when rotating drill pipe in short and medium-radius wells. This model takes into account the effects of tool joint stiffness, axial loads, and bending loads on fatigue life. Good correlations have been obtained between predicted life and failures observed in the field. This program was developed to help engineers overcome drillpipe fatigue failures encountered when rotating drillpipe in short radius wells (40-60 ft build sections).

WELCON is a well control model that handles the complex multiphase flow conditions that exist when handling gas or saltwater kicks in horizontal wells. This program is useful for developing contingency plans when planning horizontal wells and for assisting engineers when handling kicks in the field.

MUDLITE calculates wellbore hydraulics for air, mist, and foam drilling operations. This DEA-l0l model calculates pressure profiles, flow rates, cuttings lifting velocities, compressor requirements, and other parameters required to optimize underbalanced drilling operations. The program improves drilling engineers' ability to drill under-balanced by changing aerated fluid drilling from an art to a science.

Completion programs

CASING is a casing design model that calculates casing burst and collapse pressures, setting depths, and other casing design parameters for vertical, inclined, and horizontal wells. Casing design is more complicated in horizontal wells due to varying ECD's along horizontal sections and other wellbore factors.

LDRAG calculates torque and drag on liners during cementing operations. This program was developed to help engineers overcome excessive torque and drag problems encountered while cementing liners in long horizontal sections. The program calculates maximum torque on casing connections and hook loads when rotating and reciprocating liners during cementing operations to alert drillers if problems are developing during cementing operations.

CFLOAT calculates hook loads, torque, and drag when liners partially filled with air are floated into long horizontal sections. Unocal (Bell et al, 1994) pioneered the use of casing floating in horizontal wells since this is the only way to get casing to the bottom of horizontal wells with high lateral displacement-to-vertical depth ratios (4:1).

CENTRA calculates the number and location of centralizers required to centralize casing in horizontal wells. This program was developed to help completion engineers overcome cementing problems encountered in horizontal wells due to inadequate casing standoff. The program includes a database for both rigid and spring type centralizers.

CEMENT is a wellbore cementing model that handles "free fall" and other complex cementing problems encountered in horizontal wells. The program calculates ECDs throughout the well to ensure that the circulating pressures remain above formation fluid pressures and below fracture pressures during cementing operations. The program was developed to completion engineers overcome excessive ECDs encountered when cementing long horizontal wells.

GTEMP calculates wellbore temperatures during drilling, completion, and production operations. The program is used to ensure proper cement formulations, calculate wellbore temperatures for tubular thermal stress calculations, and optimize drilling procedures to ensure temperatures do not exceed the limits of downhole motors and measurement-while-drilling tools.

CWEAR is a DEA-42 casing wear model that accurately predicts casing wear throughout the well. The program is based on an Exxon model that assumes volumetric casing wear is proportional to the mechanical energy imparted to the casing by the rotating tool joint (White et al, 1987). A large DEA-42 database provides appropriate wear factors based on the abrasivity of the mud, abrasivity of the tool-joint hardmetal, and other factors. Several DEA-42 participants have credited the program with solving multi-million dollar casing wear problems.

Coiled tubing programs

Several coiled tubing (CT) programs were developed in the DEA-67 Coiled Tubing and Slimhole Drilling project to assist DEA participants in designing and conducting CT drilling and completion operations.

CDRAG calculates drag forces on CT during complex drilling and workover operations to avoid over-tensioning or buckling. The program is widely used by service companies and operators and is a major factor in the successful use of CT worldwide.

CSTRESS is a combination drag/ hydraulics model that calculates triaxial stresses and buckling limits in coiled tubing under complex loading conditions involving axial and bending loads with varying internal and external pressures.

CTLIFE was developed to help DEA participants overcome major coiled tubing fatigue failures encountered in horizontal drilling operations. The program calculates the amount of CT fatigue life used on a given field job as a function of reel diameter, gooseneck radius, internal pressure, the number of reel cycles, and other parameters. The program is based on mathematical models and experimental data published by Halliburton (Avakov et al., 1993). The program keeps track of the cumulative fatigue life on a CT string, so the remaining life is always known. The software also keeps track of changes made to the CT string (e.g. if sections of the CT are cut out or replaced). Use of the program is critical to avoid CT failures during field jobs.

TRIAX is a triaxial stress program that calculates burst and collapse pressure as a function of axial loading, bending stresses, and internal and external fluid pressures. The program was developed to help DEA participants overcome burst and collapse problems encountered in horizontal wells. The program is used by DEA participants to calculate stresses in drill strings, CT casing, downhole tools, and other tubulars used in horizontal drilling.

Drilling and completion software allows engineers to better plan and troubleshoot wells.

The use of good software can improve a drilling engineer's output by 50-100%. Few drilling engineers effectively use drilling software. The increased use of software could reduce horizontal well costs 10-25% in most areas.

This paper was presented in slightly longer form with references at the 7th Annual International Conference on Horizontal Well and Emerging Technologies - Underbalanced Drilling, Multilaterals, Completions, Geosteering; held in November, 1995, Houston.