Survey Composition

A deviation survey is composed of a number of points. The relationship between a survey contractor and the engineer associated with performing the survey is inherited from an association between activity and business_associate (Activity_BA_Inv).

The Survey class itself contains information regarding the calculation method used in calculating the points of a survey and the Declination Correction factor used for the survey. The date, mode, name, and quality of the survey are also stored. In addition to these, each survey is required to have a tie-in point. A tie-in point is a point on a survey where everything is known about a point. Some people think a survey can have more than one tie-in point, but the decision was made in the design of this model that there could only be one tie-in point for a survey.

If a survey is flagged as being the Preferred_Survey for a Borehole, this survey should be used when survey information is required for a Borehole. Note that this is a denormalization since the Preferred_Survey and Legal_Survey are held on the Borehole class itself.

A Survey is composed of points (or stations), and at these points, the minimum data that is captured is Azimuth (the angle between the vertical projection of a line of interest onto a horizontal surface and true north or magnetic north measured in a horizontal plane), Inclination (the deviation from vertical, irrespective of compass direction, expressed in degrees-Inclination is measured initially with a pendulum mechanism), and Measured_Depth or MD (the length of the wellbore as if determined by a measuring stick). From these pieces of information, other data elements such as TVD or True Vertical Depth (the vertical distance from a point in the well [usually the current or final depth] to a point at the surface) and X_Offset and Y_Offset (distance in the X and Y direction from the previous point) can be calculated.

The date and time when the point is recorded is captured in the Point_Date data element, and whether a point is a measured point or a derived point is signified in the data element Point_Type.

The two classes, Covariance_Matrix and Survey_Point_Correction, hold the data elements that together define the correction factors used in the calculation of a point.