Not less than fifteen days before the convening of the first term of the court of general sessions on or after January first and July first of each year, the jury commissioners shall proceed to draw from the jury box the number of grand jurors which the clerk of court or chief administrative judge for the circuit has determined to be sufficient in order to impanel a grand jury. The grand jurors must be randomly drawn and listed as are jurors for trials, and the jury commissioners shall not disqualify or excuse any juror drawn. Immediately after these grand jurors are drawn, the clerk of court shall issue writs of venire facias for these grand jurors, requiring their attendance on the first day of the first week of criminal court in the county on or after January first or July first of each year or at such other time as the clerk of court may designate. These writs of venire facias must be delivered immediately to the sheriff of the county or otherwise served as provided by law.