Well planning, design and construction phases are mainly concerned with three objectives:
- Well objectives as producing or exploring.
- Environmental and Safety Objectives
- Total expenditure and budget of the project
The above mentioned objectives do not come with standard specific goals and vary based on the location and environment of operations. The planning team has to correctly identify all the goals and factors that influence the project.
The first step of well planning is Well Proposal or Statement of Requirements and it is mainly concerned with the Exploration and Reservoir Engineering Department. The contents of this document include the specific objectives of the well and are can be classified as Exploration, Appraisal or Development.
The main motive behind the design of exploration wells is to assess if a subsurface prospect comprises of commercial amounts of hydrocarbons. Each exploration program can comprise of any number of wells.
Exploration wells are mainly used for data collection from potential reservoirs by making use of formation evaluation methods which might be coring, logging and well testing.
When exploration wells are drilled, they are unsure about the presence of commercial oil or gas. Also, the wells are drilled on a temporary basis and are not intended for long term use. Also, if in case oil is discovered in the exploration well, an appraisal process has to be carried out and all the alternatives must be considered, which includes the selection of development plan, implementation of the plan along with the construction of wells, infrastructure and other facilities. Usually, wells drilled offshore or the floating rigs are abandoned once the work is done. Hence, it is essential that all the objectives are achieved at a minimal cost without any compromise in the functionality and objectives.
The design, planning process and construction of appraisal wells are identical to exploration wells. However, appraisal wells are drilled only when a discovery is made, with the motive of assessing the size and viabilities of the reservoirs. They can also be drilled to obtain more information about the geology or geometry of a well present. Once the sought after information about an appraisal well is met, the drilling can be called successful.
The broad classification of wells that are drilled with the purpose of production, injection or observation of appraisal wells are known as development wells. The life cycle and operational period of development wells are much greater than appraisal wells. Development wells are drilled with various different objectives, such as flowing production, artificial lift production, injection of water or gas and to monitor the performance of a well. Over the course of time, these wells would see several work-overs, upgrades and simulations. To start with, the most basic requirement of a development well should be that the bore diameter of the well should be large enough to contain all the equipment that might be used and should reach the expected production rate without high costs or upgrades involved.