System and method for determining soil characteristics and drillstring instability during horizontal directional drilling
Disclosed is a system and method for horizontal directional drilling (HDD). The system and method utilize predictive algorithms to both characterize the soil within the borehole and to quantify instability within the drillstring. The soil characteristics are represented by a soil coefficient (α), which relates the curvature of the borehole with the length of thrust of the drill rig as well as by comparison of thrust while thrusting with torque while drilling. The value of (α) is obtained by comparison of the historical orientation of the drilling head over the length of the borehole and the borehole shape as determined by an arbitrary navigation sensor. Drillstring instability is determined as a function of historical thrust and torque efficiencies and windup over the length of the borehole.
1. A system for detecting soil characteristics within a borehole made via horizontal directional drilling, the system comprising:
a drilling assembly including a drillstring with a proximal and distal end, a drilling rig and thruster coupled to the proximal end of the drillstring, and a drilling head coupled to the distal end of the drillstring, the drilling head adapted to create a borehole through various soil types, the drillstring configured to move with respect to first (Y s ) and (Z s ) axes, and the drill head configured to move along second (Y h ) and (Z h ) axes with respect to at least one portion of the drillstring;
a first load cell operatively coupled to the drilling rig and determining the thrust applied to the drillstring at the drilling rig (Ts) and the torque applied to the drillstring at the drilling rig (Qs);
a second load cell operatively coupled to the drilling head and determining the thrust applied to the drilling head (Th) and the torque applied to the drilling head (Qh);
a first navigational sensor determining the orientation of the proximal end of the drillstring along the (Y s ) and (Z s ) axes;
an odometer operatively coupled to the drilling rig and determining the length of the drillstring (s);
a second navigational sensor determining the orientation of the drilling head along the (Y h ) and (Z h ) axes, as well as the angular orientation of the drilling head (φ);
a microprocessor in communication with the navigational sensors, load cells and odometer via a communications subsystem, the microprocessor determining the characteristics of the soil as function of (Y s ), (Z s ), (Y h ), (Z h ), while drilling, (Y s ), (Z s ), (Y h ), (Z h ) while thrusting, and (s),
wherein the microprocessor determines thrust efficiency (T h /T s ) as a function of borehole length and torque efficiency (Q h /Q s ) as a function of borehole length and wherein drillstring instability is predicted as a function of thrust efficiency and torque efficiency and windup (w).
2. The system as described in claim 1 wherein the microprocessor determines a soil coefficient (α) in accordance with the following equations:
{
ⅆ
2
y
ⅆ
s
2
=
α
∫
0
L
sin
φ
(
s
)
ⅆ
s
ⅆ
2
z
ⅆ
s
2
=
α
∫
0
L
cos
φ
(
s
)
ⅆ
s
,
wherein L is the length of well bore.
3. The system as described in claim 1 wherein the microprocessor determines a soil coefficient (α) in accordance with the following equation:
ⅆ
2
y
ⅆ
s
2
=
α
∫
s
=
s
0
-
L
s
=
s
0
sin
φ
(
s
)
ⅆ
s
,
wherein L is the length of well bore, and S 0 is the current odometer reading.
4. The system as described in claim 1 wherein the microprocessor determines a soil coefficient (α) in accordance with the following equation:
ⅆ
2
z
ⅆ
s
2
=
α
∫
s
=
s
0
-
L
s
=
s
0
sin
φ
(
s
)
ⅆ
s
,
wherein L is the length of well bore, and S 0 is the current odometer reading.
5. The system as described in claim 1 wherein the microprocessor predicts instability within the drillstring as a function of (Ts), (Qs), (Th), and (Qh).
6. The system as described in claim 1 further comprising:
a database of experimental determinations correlating drillstring instability with thrust efficiency and torque efficiency and windup at specified borehole lengths, wherein borehole instability is predicted with reference to the database.
7. The system as described in claim 1 wherein the navigational sensors include inclinometers and accelerometers.
8. The system as described in claim 1 wherein the first navigational sensor is positioned within the drilling rig.
9. The system as described in claim 1 wherein the second navigational sensor is positioned adjacent the drilling head.