Well Proposal Outline
  • ❑ Planning and Drilling an Exploration Well
  • ❑ Well objectives:
    • ❑ Prove that oil and gas both exist in the reservoir, obtain smaples of each for analysis, and measure the fluid pressures in the reservior
    • ❑ Determine the depth of the gas-oil and oil-water contacts
    • ❑ Take core samlpes in the oil part of the reservoir
    • ❑ Test the oil later to measure the following
      • ❑ maximum rate at which the oil can flow before sand starts to be produced
      • ❑ the maximum possible production rate
      • ❑ internal reservoir characteristics such as permeability, porosity, internal boundaries, pressures, and temperatures
      • ❑ damage to the reservoir from the drilling operation- the mechanical skin
  • ❑ Well proposal
    • ❑ Type of well (exploration) and well objectives
    • ❑ Essential design data
      • ❑ Surface location
      • ❑ downhole targets to hit- position, depth and the acceptable margin for error
      • ❑ depths and descriptions of the downhole strata
      • ❑ expected strengths of the formations downhole and rpessures of the fluids inside the rocks
      • ❑ what information is required from the well
      • ❑ whether core samples of rock should be obtained and at what depths
      • ❑ what should happen to the well after operations are complete
      • ❑ outline of the completion design for the well
  • ❑ Well Review Criteria
    • ❑ Proposal is logical and objectives are achievable
    • ❑ Essential well design data is complete and there are no ambiguities or omissions
    • ❑ The directional targets that the well needs to hit are as large as possible; the smaller the target, the more the well is likely to cost
    • ❑ The proposal doesn't give rise to any inherent hazards that might create a danger to personnel, the rig, or the well
    • ❑ The well's negative impact on the environment is minimal.
  • ❑ Designing the Well
    • ❑ "defines the final status of the well"
    • ❑ Diameter of the hole through the formation
      • ❑ Well progresses in a series of "hole sections" Figure 3-3
        drilled progressively in smaller hole sizes. While there will be a ideal mminimum hole size to obtain all of the desired information, it is possible that he essential information could be obtained in a smaller size hole. A well might be planned to finish in 8.5" diameter hole (which would all of the logs and tests to be run) but it might also be possible to run the bare essential tools in a6" diameter (or smaller) hole. This allows for a contingency= if there are unanticipated problems while drilling and an extra set of casing pipe has to be set, the essential objectives can still be met.
    • ❑ Casing Design
      • ❑ bottom of string: casing shoe ideally cemented in hard, strong impermeable formation- unfractured shale or well consolidated sandstone
        formation in which the casing shoe is cemented is very important because it must be able to withstand pressure in the event of a kick. If it should break, it will fracture the formation possibly all the way to the surface, allowing pressureized hydrocarbons to travel up, out of the seabed or the ground around the rig, where it might ignite.
      • ❑ maximum depth that can be safely drilled below any particular casing, dependson
        • ❑ formation strength at the casing shoe
        • ❑ density of the drilling fluid in the well
        • ❑ hole diameter
        • ❑ maximum volume of formation fluid that can be allowed into the well (influx volume)
        • ❑ density of the formation fluid that enters the well in a kick (kick tolerance calculations)
          By knowing which formations are suitable for the casing shoe and calculating how far to drill before the kick tolerance becomes too small, the ideal depth to set each asing can be determined. This also dictates how many different hole sections (and casings) are needed
    • ❑ Well program
      • ❑ instruct/"advise" the rig on how to implement the design most efficiently
        • ❑ drilling supervisors in charge of the rig operations may need to deviate significantly from the program if safety or efficiency might otherwise suffer
      • ❑ program should contain the information behind all the major decisions made, so that the original information can be combined with new information to make the most informed decisions possible. What should happen and why.
      • ❑ May include following sections
        • ❑ General Information
          1. Which country, which exploration block (play)? name of drilling rig, program issue date, who the program was written by, and who approved it 2. Which offset wells were used for data input 3. A statement on shallow gas pocket of gas can be found very close to the surface. the first string casing consists of a very thick walled pipe, (>1inch), hammered into the ground with a pile driver; conducts fluid back up to the rig when drilling starts. Shallow gas is the most serious type of danger to the rig and the people. If it is hit and the well kicks, things will happen very quickly; all the drilling fluid in teh well can be blown out so that the gas is flowing freely out of htw well. many rocks or large volumes of sand or other material will come out with the gas and this can erode steel lines very quickly, allowing gas to flow within the rig structure. Shallow gas can also contain hydrogen sulfide. To avoid hitting shallow gas: Carry out special type of shallow seismic survey If the well is offshore, first drill a small hole at the proposed well location from aspecial kind of floating rig that will quickly move away if shallow gas is hit Examine the recoreds of offset wells and see if shallow gas was encountered in any of them
        • ❑ Well objectives
          Primary Objectives Secondary Objectives A graph showing the anticipated well depth at each day of operation Detailed cost estimate
        • ❑ Potential Hazards
          Hazards inherent to the location weather
        • ❑ Surface location and how the rig is to be positioned
          Lat/Long of the rig with error margin "datum level for depth"- mean sea level, lowest astronomical tide water depth for offshore
        • ❑ General notes
          Required drilling pratices specific operational procedures recommended operation sequence of events what drill bits are recommended what bottom hole assemblies special requirements
          • ❑ references to government regulations, company policies, oilfield standards
          • ❑ reporting techniques
          • ❑ quality control and ata recording requirements
          • ❑ diagram of the completed well
          • ❑ equipment checklists and suppliers of each item
          • ❑ cost estimating information to allow the well cost to be calculated each day
        • ❑ Drilling Notes for each hole section
          • ❑ potential hazards or problems, how to avoid them, and now to recover from them
          • ❑ required drilling practices
          • ❑ recommended operational sequence of events
          • ❑ kick tolerance information
          • ❑ what drill bits are recommended
          • ❑ what bottom hole assemblies are recommended
          • ❑ any special requirements
        • ❑ Drilling fluid design and maintenance requirements for the whole well
          circulating fluid must keep well bore stable (hole that stays the same diameter of teh bit that drilled it and perform many other functions
        • ❑ Wellbore trajectory information
          Everthing that defines teh path that the wellbore should follow must be known; vertical section diagrams and from above (plan view) must be included. The actual path of the wellbore may be marked on the same chart to show deviation
        • ❑ Casing design for the well and how the casing are to be cemented in place
          outside diameter of the pipe thickness of pipe what sort of threads to screw the casing together type of steel to make the casing types of tools to screw into casing
        • ❑ Geological information on the formations expected to be penetrated
          estimate the strengths of rocks pore pressure formation lithologies, permeability, porosity, composition of pre fluids, depths, thickness, and teh stresses present in the rock are all valuable
        • ❑ Logging and coring program- what electrical logs to run and if the well is to have a core sample cut, the relevant dtails
          tools can be run into the well on special electrical clabes (electric logs) measure many different types of formation characteristics
        • ❑ Well completion design and program
          need to know the outside diameter of the completion or test tubing string.
        • ❑ Well test information, if the well is to be production tested
          test program for production
        • ❑ Status of the well when the rig has finished work
          what should be the status of the well when they finish their work. unperforated, perforated then killed with clean completion fluid