Fix for straight hole conditions.

In wells with straight hole sections where the angle between
subsequent survey stations is 0 degrees, a ZeroDivisionError occurred.

This issue was flagged in #54.

wellpathpy/position_log.py

@@ -483,7 +483,10 @@ def deviation(self):
             d = np.linalg.norm(v1)
             incs.append(i2)
             azis.append(a2)
-            mds.append(d * alpha / np.sin(alpha))
+            if alpha == 0:
+                mds.append(d)
+            else:
+                mds.append(d * alpha / np.sin(alpha))
             # The current lower station is the upper station in the next
             # segment.
             i1 = i2

wellpathpy/test/fixtures/straight_dev_section.csv

@@ -0,0 +1,7 @@
+md,inc,azi
+0,0,0
+50,0,0
+100,2,0
+150,2,0
+200,2,0
+250,2,0

wellpathpy/test/fixtures/straight_vert_section.csv

@@ -0,0 +1,7 @@
+md,inc,azi
+0,0,0
+190,0,0
+222,0,0
+360,0.3,256.5
+390,0.2,124.8
+419,0.4,114.3

wellpathpy/test/test_calculations.py

@@ -12,6 +12,9 @@
 # import test well data
 well9 = np.loadtxt('./wellpathpy/test/fixtures/well9.csv', delimiter=",", skiprows=1)
 well10 = np.loadtxt('./wellpathpy/test/fixtures/well10.csv', delimiter=",", skiprows=1)
+straight_vert = np.loadtxt('./wellpathpy/test/fixtures/straight_vert_section.csv', delimiter=",", skiprows=1)
+straight_deviated = np.loadtxt('./wellpathpy/test/fixtures/straight_dev_section.csv', delimiter=",", skiprows=1)
+
 # get data series
 well9_true_md_m = well9[:,0] * 0.3048 # converting feet to meters
 well9_true_inc = well9[:,1]
@@ -196,3 +199,60 @@ def test_roundtrip(atol = 0.01):
     np.testing.assert_allclose(pos.depth,    well9_true_tvd_m,    atol=1)
     np.testing.assert_allclose(pos.northing, well9_true_northing, atol=1)
     np.testing.assert_allclose(pos.easting,  well9_true_easting,  atol=1)
+
+def test_roundtrip_vertical_straight_hole(atol = 0.01):
+    """
+    This pretty much only tests the mincurve, but packed in the
+    deviation+position_log interface
+
+    For a vertical straight hole, the inclination stays 0, but
+    azimuth can rotate freely.
+    """
+    md_m = straight_vert[:, 0] * 0.3048 # converting feet to meters
+    inc  = straight_vert[:, 1]
+    azi  = straight_vert[:, 2]
+    tvd_m    = straight_vert[:, 0] * 0.3048 # converting feet to meters
+    easting  = [0, 0, 0, 0, 0, 0]
+    northing = [0, 0, 0, 0, 0, 0]
+
+    # the hole is vertical
+    assert np.all(inc) == 0
+
+    dev = deviation(md_m, inc, azi)
+    pos = dev.minimum_curvature()
+    dev2 = pos.deviation()
+    np.testing.assert_allclose(dev.md,  dev2.md,  atol = atol)
+    np.testing.assert_allclose(dev.inc, dev2.inc, atol = atol)
+    np.testing.assert_allclose(dev.azi, dev2.azi, atol = atol)
+
+    pos.to_wellhead(surface_northing = 0.0, surface_easting = 0.0, inplace = True)
+    np.testing.assert_allclose(pos.depth,    tvd_m,    atol=1)
+    np.testing.assert_allclose(pos.northing, northing, atol=1)
+    np.testing.assert_allclose(pos.easting,  easting,  atol=1)
+
+def test_roundtrip_deviated_straight_hole(atol = 0.01):
+    """
+    This pretty much only tests the mincurve, but packed in the
+    deviation+position_log interface
+
+    For a deviated straight hole, MD should increase, but inc
+    and azi must remain constant.
+    """
+    md_m  = straight_deviated[:, 0]
+    inc   = straight_deviated[:, 1]
+    azi   = straight_deviated[:, 2]
+    tvd_m = np.array([0., 50., 99.989847, 149.959388, 199.928929, 249.898471])
+    easting = [0, 0, 0, 0, 0, 0]
+    northing = np.array([0., 0., 0.872576, 2.617551, 4.362526, 6.107501])
+
+    dev = deviation(md_m, inc, azi)
+    pos = dev.minimum_curvature()
+    dev2 = pos.deviation()
+    np.testing.assert_allclose(dev.md,  dev2.md,  atol = atol)
+    np.testing.assert_allclose(dev.inc, dev2.inc, atol = atol)
+    np.testing.assert_allclose(dev.azi, dev2.azi, atol = atol)
+
+    pos.to_wellhead(surface_northing = 0.0, surface_easting = 0.0, inplace = True)
+    np.testing.assert_allclose(pos.depth,    tvd_m,    atol=1)
+    np.testing.assert_allclose(pos.northing, northing, atol=1)
+    np.testing.assert_allclose(pos.easting,  easting,  atol=1)

wellpathpy/test/test_position_log.py

@@ -38,42 +38,3 @@ def test_copy():
     copy = original.copy()
     original.depth += 10
     np.testing.assert_equal([1,2,3,4], copy.depth)
-
-def test_straight_down_segment_preserves_depth():
-    """
-    When the well is straight down, the vertical depth and measured depth
-    should increase at the same rate.
-    """
-    md  = [0, 3, 7]
-    inc = [0, 0, 0]
-    azi = [0, 0, 0]
-
-    pos = deviation(md, inc, azi).minimum_curvature()
-    np.testing.assert_array_equal(md, pos.depth)
-    np.testing.assert_array_equal([0, 0, 0], pos.northing)
-    np.testing.assert_array_equal([0, 0, 0], pos.easting)
-
-def test_straight_nonvertical_segment():
-    """
-    The well has a constant inclination which means delta(md) > delta(vd), the
-    path is not straight down. This doesn't test for the path going back up.
-    """
-    md  = np.array([1,  3,  7])
-    inc = np.array([30, 30, 30])
-    azi = np.array([0, 0, 0])
-
-    pos = deviation(md, inc, azi).minimum_curvature()
-    delta_md = md[1:] - md[:-1]
-    delta_vd = pos.depth[1:] - pos.depth[:-1]
-    assert (delta_md > delta_vd).all()
-
-@pytest.mark.xfail(strict = True)
-def test_straight_hole():
-    md = np.array([0, 10, 20]).reshape(3, 1)
-    inc = azi = np.zeros((3, 1))
-    dev = deviation(md=md, inc=inc, azi=azi)
-    step = 10
-    depths = list(range(0, int(dev.md[-1]) + 10, step))
-    with np.errstate(invalid='raise'):
-        pos = dev.minimum_curvature().resample(depths=depths)
-        dev2 = pos.deviation()