Well Planning - Lecture notes 1 PDF

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Well Planning for Drilling Engineer...

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Well Planning-An Introduction Soumyadip Choudhury Asst. Professor Dept. of Petroleum Engineering A.H.C.E.T

Introduction • Well planning is perhaps the most demanding aspect of drilling engineering. It requires the integration of : • Engineering Principles • Corporate or Personal philosophies • Experience Factors

• The end objective for any well planner is to design a safely drilled minimum-cost hole that satisfies the reservoir engineer's requirements for oil and gas production. • A skilled well planner must namely exhibit 3 traits, i.e. • They are experienced drilling personnel. • They utilize available engineering tools, engineering software etc. • Having a “Sherlock Holmes” approach !!

Objective The objective of Well Planning is to formulate a program for designing a well that has the following characteristics: • Safety • Minimum Cost • Usable

Safety • Safety should be given the highest priority in well planning. • Personnel considerations must be placed above all other aspects of the plan. • Sometimes during the drilling of a well, the plan must be modified in order to accommodate personnel safety. • Failure to stress crew safety has resulted in accidents and in extreme cases loss of life.

Safety • The well plan must be designed to minimize the risk of blowouts.

• The Well Plan must also incorporate other factors which may create problems. • This design requirement must be adhered to vigorously in all

aspects of the plan.

Minimum Cost • A valid objective of the well planning process is to minimize the cost of the well without jeopardizing the safety aspects. • In most cases, costs can be reduced to a certain level as additional effort is given to the planning. • It is not noble to build "steel monuments" in the name of safety if the additional expense is not required. • On the other hand, money should be spent as necessary in order to develop a safe system.

Usable Hole • Drilling a hole up to a target depth is considered to be satisfactory if the hole is usable. • The term “usable*” implies that: • The hole diameter is sufficiently large so an adequate completion can be made. • The hole or producing formation is not irreparably damaged. *Note that this requirement of the well planning process can be difficult to achieve' in abnormal pressure, deep. zones that can cause hole geometry or mud problems.

Factors affecting the Well Plan While designing the Well Plan, the following factors should be kept in mind:

• Well Type • Formation Pressure

• Planning Cost

Well Types Wells mat be classified into the following types depending upon the purpose and the degree of information available prior drilling. Well Type

Characteristics

Wildcat

No known (or little) geological foundation for site selection.

Exploratory

Site selection based on seismic data, satellite surveys, etc.; no known drilling data in the prospective horizon.

Well Types Well Type

Characteristics

Step-out

Delineates the reservoir's boundaries; after the exploratory drilled discovery(s); site selection usually based on seismic data.

Infill

Drills the known productive portions of the reservoir; site selection usually based on patterns, drainage radius, etc.

Re-entry

Existing well reentered to deepen, sidetrack, rework, or recomplete; various amounts of planning required, depending on purpose of reentry.

Formation Pressure • The formation, or pore, pressure encountered by the well significantly affects the well plan. • The pressures may be classified as: • Normal • Abnormal (High) • Sub-normal (Low)

• Normal pressure wells generally do not create planning problems. The mud weights are in the range of 8.5-9.5 ppg. • Kicks and blowout prevention problems should be minimized but not eliminated altogether as casing requirements can be stringent even in normal pressure wells deeper than 20,000 ft due to tension/collapse design constraints.

Sub-normal Pressure • Subnormal pressure wells may require setting additional casing strings to cover weak or low pressure zones. • The

lower-than-normal

pressures may result from

geological or tectonic factors or from pressure depletion in producing intervals. • The design considerations can be demanding if other sections of the well are abnormal pressured.

Abnormal Pressure • Abnormal pressures affects the well plan in the following areas: • • • •

casing and tubing design mud weight and type selection casing setting depth selection cement planning

• Abnormal Pressure may also result in the following problems: • kicks and blowouts • differential pressure pipe sticking • lost circulation resulting from high mud weights • heaving shale

Planning Cost • The costs required to plan a well properly are insignificant in comparison to the actual drilling costs. • In many cases, less than $1,000 is spent in planning a $1 million well. • This represents 1\10 of 1% of the well costs.

Well Cost vs. Well Planning effort

Activities before start of Drilling Operation • Release of location. • Survey of surface/subsea location. Sometimes the cost can be reduced by a small change in surface location. • Civil works and foundation for onshore drill-site and soil coring/sea bed survey in case of offshore well. • Preparation of Geo- Technical Order (GTO). • Preparation of complete well plan/programme. • Preparation of bill of material and initiation of purchase procedure, if required. • Procedures from obtaining sanction for purchase to receipt of material. • Rig allocation and its shifting to the new location.

INPUT DATA FOR WELL PLANNING • The objective of the well • Primary, Secondary & Other

• Well data package consisting of: • Seismic Data • Geological Information (Tentative Litho-column) • Location Map • • • • •

• • • •

Co-ordinates & Surface Location Well Name Well ID Seismic Lines ( Inline & Crossline ) KB – GL (Onshore) / Air Gap & Water Depth (Offshore)

Structural Map Expected Pore Pressure Offset and Correlation Logs Formation type, top and thickness

INPUT DATA FOR WELL PLANNING • Offset and correlated drilled wells data consisting of: Bit Report Mud Report Mud Logging Report Drilling Report Complication Report ( If CO2 , H2S etc. is present, if a fault or a salt zone might be encountered ) • Well Completion Report ( History of complications from previously drilled wells) • • • • •

• Production & Injection Histories • Proposed logging, testing and coring programmes. • Government reflection and Company's policy.

Geotechnical Order (GTO) After the various input data are thoroughly analyzed, a Geotechnical Order (GTO) is prepared. G.T.O. furnishes the following details: • General data like well name, well number, area, location, water depth, elevation, well type, category, objectives of the well etc. • Geological data consists of following details: • • • • • • • • • • • •

Depth Age Formation Lithology Interval of coring Electro logging Collection of cuttings Angle of Dip Oil/gas shows Formation pressure Formation temperature Mud loss/caving

Geotechnical Order (GTO) • Mud parameters consist of: • • • • • •

Type of mud Specific gravity Viscosity pH Percentage of sand Filtration loss

• Drilling data includes: • • • • • • • • • • • •

Casing policy and rise of cement Type of drilling Type and size of bit Number of bits expected Meterage per bit Weight on bit RPM of rotary Stand-pipe pressure Pump discharge Bit nozzle details Drilling time Remarks, if any

Drilling Programme Preparation The preparation of good Drilling Programme is very vital for safe and effective drilling operation. Drilling Programme can be broken down into 12 main sections: • Well details • Well objectives • Casing policy • Wellhead selection • BOP requirements • Cementing programme • Deviation programme • Survey requirement • Mud programme

Drilling Programme Preparation • Bit and Hydraulics programme • Evaluation requirements • Estimation of well cost

Types of Drilling • Based upon the nature of motion imparted to the bit, drilling may be classified into the following types: • Cable Tool Drilling • Rotary Drilling

• Based upon the location of the payzone, drilling may be categorized into the following types: • Vertical Drilling • Directional Drilling    

Horizontal Drilling Slant Drilling Type I , II, III, IV well. Designer Wells

Cable Tool Drilling

The First Photographic evidence of the American Oil Well Drilling – “ The Historic Drake Well located in Titusville near Pennsylvania”

Cable Tool Drilling • Reportedly the Cable Tool (also called the churn or percussion drilling ) method was first used by the Chinese. • In this method the drilling action is accomplished by the pounding action of the steel bit which is alternately raised by the steel cable and allowed to fall delivering sharp blows to the hole bottom. • This uses the same principle as that of an air hammer or when driving nails through a block using a hammer.

Rotary Drilling Method

Directional drilling

Directional drilling • Controlled directional drilling is defined by the API as: “The art and science involving the intentional deflection of a wellbore in a specific direction in order to reach a predetermined objective below the surface of the earth.” Today, it is much more science than art....