Well Seeker X: U-Zontal Well Plans - Minimum Curvature Limitation

Introduction

Minimum curvature is the industry standard method of calculating wellbore position based upon survey data and is also the calculation used in most planning methods. This tech note will inform the user of one specific scenario where the minimum curvature calculation method will yield some unexpected results in u-zontal well plans, explain why this is happening and provide a solution.

Problem

When planning an exactly 180° azimuth change, on 1 row of the plan, using ADJ_MD as the planning method, the minimum curvature calculation can theoretically come up with multiple different results.

In the example below the well planner wants the horizontal well to make a flat turn from 270° to 90° azimuth, holding 90° inclination. The minimum curvature calculation provides a mathematically correct result for this, but it does not match the well planner’s intended path.

This scenario can happen when a plan is imported from a Compass edm file (as the import planning method is ADJ_MD), when well planning in Well Seeker, or when using the Create Offset Plan tool.

Solution

In order to resolve this issue we can tackle any one of three things:

1. All of the turn occurs in 1 row of the plan

2. Exactly 180° azimuth change

3. Using ADJ_MD as the planning method

As changing the azimuth, or the planning method are unlikely to be acceptable solutions in most cases we will focus on editing the plan so that the 180° azimuth change occurs over multiple rows.

Add an Intermediate Point

If we take the same plan as in the earlier example and simply add an interpolated point from the intended curve, the calculated results are as the user intended.

Create Offset Plan – Adjust Dip on Azi Option

If this issue occurs when using the Create Offset Plan tool, ensuring that the Adjust dip on azi option is selected will resolve the issue (as this calculates multiple interpolated points as the azimuth changes)